You can get a 30 day, fully functional trial of XSI from:

Download

1. Import the mesh you want to map, and isolate the part you want to work with. I chose the V4 head, about 20k polys.

1. Build a proxy head, 200 polys. The closer to the original the better but low poly enough to be easily tweaked. Or use one of XSI's premade heads and tweak it.

(contd)

1. UV map proxy head with a basic cylinder projection.

1. Tweak proxy UVs and make corrections.

(contd.)

1. Transfer UVs from proxy to original head with GATOR.

1. UVs on high poly head from transfer.

(contd.)

1. XSI maintains a live connection to low poly UVs

1. tweak till you're happy.

Of course this is a quick example so it still needs work, but the whole thing took like 15 mins. At no point did i have to touch the high rez mesh and i can keep tweaking the low rez mesh till i get a perfect map on the high rez one. Once you have a proxy you like, you can also reuse it for other meshes. If you have trouble working on the whole mesh, you can cut it into parts and combine their maps in the end.

IIRC the full V4 body map i use now took me about 2-3 days with this method.

Hope it helps someone and that it convinces more people to take a look at XSI. There's lots of cool tools like this in it.

That's a pretty powerful UVmapping technique, thanks for the info.  Checking around for alternatives it seems there is a plugin for Maya (which I don't have):
http://www.tsplines.com/resources/uvtut.php

Silo can do it (and I don't have it either):
http://nevercenter.com/support/help/index.html?create_uv_proxy.htm

Not having any luck finding a corespondent for Cinema 4D but I'll keep looking,  Thanks for the info, this is a pretty impressive technique.

Okay, as it turns out Cinema's MOCCA module (which I DO have) contains a subset of tools called VAMP (Vertex Map Manager) - transfers bones, weights, UVmaps, morphs! between different objects of similar shape but different topology - very neato.  FYI and thanks for the initial info.  Handy stuff.

Yep most high end apps have tools to do this, glad you found the C4D versions.