AlLewis, this may not help you but its something i have dealt with before and found it works. When you do the render do you have other things running, EG: anti-virus, firewall software, system monitors, messenger (yahoo or msn) or anything else running in the background that can take up ram usage or cpu usage. If so try closing them down. Now for your jpg problem, i use one program for converting images to jpg and have done for over 6 years without any trouble, mind you its not free and i got what i paid for(a great program). I use ACDSee. I do my renders in bmp then convert them in acdsee.

I will list the render settings i use and maybe you can give these a try.

General
Speed = Software Render
Style = Normal
Dimensions = Presets(Display standard/cine 35mm(4:3))
Pixel Dimensions 1024x768
Timeline = Still Image

Advanced
Use Software - 3Delight
Bucket Order : Horizontal
Bucket size : 16
Max Raytrace : 6
Pixel samples(x): 4
Pixel samples(y): 4

Now i am no expert on this program nor do i claim to be on anything in the 3d art world but i have found over the last 2 years i have been involved with it plus using D|S that if you use a few lights, reflections and shadows in your render they will take quite some time to do and may cause problems on some computer systems. You may need to look at these few pointers i have given you and see how things go.

Goodluck hope you sort it all out.

I have opinions of my own -- strong opinions -- but I don't always agree with them.