It's always a good idea to upgrade and if your PC has an AGP slot, which is highly likely, then go for it.
Why are you going for the latest RADEON...when you say latest Radeon, do you mean the 9700 or 9800 ect, which are very expensive? Baring in mind that a lot of games don't actually fully use the power of top spec cards.
Can you tell me why you have opted for Radeon instead of G-Force? Just curious.
If you are going to spend a few bob I would have opted for the G-Force Ti4200, this will be a major jump from your current card, without burning a huge hole in your purse.
What ammount of ram do you have?
Im a nosey we git...I just like to build a picture, lol!