From the readme:
"This project is non-official patch fo Jagged Alliance 2. The main idea of the patch is changing of the screen resolution from 640x480 to 800x600. IMHO, the game image became fine at the displays larger than 14'' Characters look less pixelized at my 15'' screen. The visible area became larger. Some cosmetic changes also were made. The gameplay was not modified, and I hope its hadn't changed. This will be realised later;)
While using any material from this archive references to the authorship and ja2.ru & ja2.org are obligatory."
Download
http://www.sininen.de/ja2-800x600-setup-1.2-eng.rar
To be honest, I installed it and barely noticed any ingame difference. I'd not been playing it long before installing this so I wasn't really used to 640*480 either. There are superficial differences, the title & options screens are a bit wonky, the background image is off centre but everything seems to still work. Also the laptop background has now changed to a shameless ad for a fallout mod that was probably never finished.
it might be handy for those who prefer to play vanilla before experimenting with chocolate, rum & raisin or horse

Ahh silly me. As an addendum, the resolution patch creates a new EXE, when that's run everything seems to be in the right places and functional so it's a must-download for people like me who want the higher res version without the 1.13 mod (I always play the unmodded versions first except for little things like resolution mods)

Is there an 800x600 res patch for JA2:UB? Thanks.

I couldn't find any mention of one I'm afraid. I don't actually have it myself so I'm not sure if its a seperate EXE or just a new option in the JA2 menu. If the latter then it shouldn't be a problem. If it's the former, you MIGHT be able to install that mod anyway, the games are very probably based on the same engine and so would likely share the same resources.
Probably worth an experiment as long as you back up your saves and don't mind a reinstall if it goes wrong.

This is an old post, but I was playing around with this today, and noticed you can just not include the Laptop directory, to
rid yourself of the shameless promotion.

So far I'm preferring this resolution patch to Stracciatella. Stracciatella, for whatever reason, causes my game to lag. Might just be an issue with the 64-bit version.

Update: This 800x600 patch has one major flaw. Apparently enemies no longer drop items whatsoever. Looks like this resolution fix is some kind of bastardized version of an older 1.13 exe. I've since moved to Stracciatella - using the 32-bit version.