Disclaimer:  I'm confident that my way is by no means the best way to do it and am certain that there is a better way to do it.  That being said...

(Assuming you've got all of your textures saved as .jpgs or .psd, etc...)  Also, assuming that you're using Windows as opposed to Mac.

First create a folder in Textures under the runtime directory.  Example c:program filescurious labsposer 5runtimetexturesPropschick.

The way I've done it (and I don't do it very often) is to go to the Pose directory in the runtimelibraries folder and pick out any ol' existing .pz2 file which is associated with applying textures (materials.)  Right-click on it and choose Open With....

Select either Word Pad or Note Pad to open the file.  Start scrolling down and find all of the instances where you would see something like the following:

textureMap ":Runtime:textures:Stegy:BaseTexture_Body.jpg"

Replace it with your own file information, perhaps something like this:

textureMap ":Runtime:textures:PropsChick:BaseTexture_Body.jpg"

After you've done all of your replacements, do a Save As to a new file name.  The only thing left to do will be to create .png thumbnail to go along with it. You can do that by rendering a scene with your new texture in a 91x91 window and saving it as a .png picture.  Just make sure that it has the same name as your newly created .pz2 file.  That's it in a very brief nutshell.

Edit:  optional stuff: You can also create a .rsr file (alternate thumbnail file format).  Just go to the Freestuff and do a search for "RSR".  Look for a utility called, "PNG TO RSR"

I have P4, P5, and P6 all installed on the same machine.  No problems to speak of.  The only thing that annoys me sometimes is when I double-click on a .pz3 and it automatically opens, for example, with P6 when my intention was to open it with P5 (just a minor thing).  The advantage is that you can add the P4 runtime to P5.  That way, you don't have to move all of your collected P4 content over to the P5 runtime folders.

I've used P4 successfully, (but very limitedly) on my eMac with 10.3.9. I've also had a few (but not many) problems with P5.

The only way that I could reproduce the "isn't a valid Poser file" issue was on my Mac BEFORE applying SR4 for OSX (Mac) available from e-frontier.com. 

After applying the patch, it seemed to work just fine.  However, I also re-downloaded and installed the Kyoko Hair from Koz's website at the same time.  Again, it has always worked on my Windows machine.

So, I woud have to concur with Acadia's posting, unless I missed a step or two. I hope that you get it sorted out!  Koz has some of the best hair available!

Are you using a Mac? 

 - Just a guess... 

I noticed that in the download zip files (for example Kyoko hair), he includes an extra folder called, "XtraStuff.Mac".  It only contains the Character and Pose stuff, but not the Geometries and Textures.  Is it possible that you forgot to copy over the Geometries and/or Textures stuff from the main "Runtime" Folder?

Kyoko hair works just fine on my Windows machine.  I'm downloading a free copy of Poser 5 for my Mac to test it out.  (How fortuitous that Content Paradise is giving it away for free!)  I'll let you know what happens!

What kinds of problems are you having?  Koz gives a tip on his site regarding the use of texture filtering here in P5:  http://www.digitalbabes2.com/dload/texturefiltering.html  Maybe that will help?

Can you post a screen shot?  Or is it a problem with loading? 

I believe the vt,  vn, & f lines have to do with uv mapping. 

Example: a very simple plane before taking into a UV Mapping program:

g plane

v 0 0 0
v 10 0 0
v 0 10 0
v 10 10 0

vt 0 0
vt 1 0
vt 0 1
vt 1 1

vn 0 0 1
vn 0 0 1
vn 0 0 1
vn 0 0 1

f 1/1/1 2/2/2 4/4/4 3/3/3

After UV-mapping and changing it to a spherical mapping:

v 0.00000000 0.00000000 0.00000000
v 10.00000000 0.00000000 0.00000000
v 0.00000000 10.00000000 0.00000000
v 10.00000000 10.00000000 0.00000000

vt 0.02500000 0.02500000
vt 0.97500002 0.02500000
vt 0.97500002 0.97500002
vt 0.02500000 0.97500002

vn 0.00000000 0.00000000 1.00000000
vn 0.00000000 0.00000000 1.00000000
vn 0.00000000 0.00000000 1.00000000
vn 0.00000000 0.00000000 1.00000000

g plane

f 1/1/1 2/2/2 4/3/4 3/4/3

Check out this also.  Kinda the same thing.

http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2313758

Just a guess - you can maybe try reversing the normals on whatever material group is for the sign. 

Seems like they had to add support for Poser when they acquired Eovia.  Carrara has Transposer which allows you to pull in .pz3 files into Carrara and render them. 

I was able to purchase Pro Pack a few months ago from Fry's Outpost.  Check here:

http://shop3.outpost.com/product/3624945?site=sr:SEARCH:MAIN_RSLT_PG

It says to call for availability, so their stock might be dwindling down.

I started out using Carrara 3.  Now, I do just about everything in Rhino.  I got hooked on it after trying out their demo.  It seems to have the most intuitive interface/flow to me.  Problem is that it's Nurbs and doesn't do meshes as cleanly as other apps.  So, I usually "refine" my meshes in Carrara. 

HI Joe,

I have used this book:  Secrets of Figure Creation with Poser 5 to get me started.  I used it to help me rig my "Bender" figure and a few other things which I created in Rhino.

Book link:  http://www.amazon.com/gp/product/0240519299/sr=8-10/qid=1145022879/ref=pd_bbs_10/002-1534182-1883217?%5Fencoding=UTF8

Bender Image Link:  http://www.renderosity.com/viewed.ez?galleryid=969417&Start=1&Artist=Stegy&ByArtist=Yes

Also, Dr. Geep probably has some good stuff in his tutorials:

Dr Geep Link:  http://myweb.cableone.net/geep/Welcome/1_Welcome.htm