Just because R* didn't confirmed a PC version it doesn't mean there won't be one ... Remember that GTA games sell very well so don't making one is the worst decision that R* could ever make, they'd just lose money, money that could be used for the upcoming GTA titles, and trust me R* wants money. Also releasing the PC version the same time with the console version would kinda ruin the games sales for consoles ( M$ and Sony would be pissed because they want to force you into buying a console for playing console games ). 5 to 10 dollars from a game's price go to M$ and Sony. I think R* will announce the PC version June 2008 and release it this October.
Yep. There was a topic back at GTAF about it so I just posted the link to the video ... You can check the video clicking the link to the topic mentioned above by mark866.
Now, ontopic, I don't think you'd need a powerfull PC, sure it won't run well on old machines but upgrading your PC won't cost you too much
With $75-100 you can buy about 4GB of RAM, with $300 you can buy a powerfull graphics card ( 8800 GTS ) and with about $200 you could buy a powerfull processor ( AMD Athlon X2 6000+ ) ... And it would last you more than a console, plus you'll be able to play on higher resolutions and better framerate ...