I've been searching Google but it only gives answers for GTA4 and since I've bought the GTA Pack on Steam, I'd like to play the older games but in a better resolution than 800x600. Is there any way to do this? Maybe a program that forces them to this resolution or perhaps an ini change?
A game needs to internally support a resolution in order to produce graphics at that resolution—there's no way to force a resolution that's unsupported without recoding parts of the graphics engine itself. This can be done with a lot of skill and code injection, but my searches turn up nothing: it doesn't look like anyone has done a graphics engine enhancer for GTA1.
Use ThirteenAG's widescreen fix (the screenshots are captured in 1,920 × 1,080).