If it can run GS Mode Selector (by using FMCB) then just get some component cables.
I just bought a component cable a few days ago on eBay for $5. Got it today and the difference is amazing. I can actually read the letters on an HDTV, weird right? It makes it really crisp.
That's just standard 480i though (or 480p if the game supports it)
I mentioned GSMode Selector because using that you can force the PS2 to upscale to 480p, 720p, or 1080i if you wanted to. I don't see much of a difference between them though, because it isn't true HD and nothing can ever make it that way, so I just keep it unmodified @ 480i.