Well You'll see night and day with XPS 410 with 2 Gigs of RAM.
as someone said don't turn off the firewall if connectect to the internet.

But when playing games the most important thing is the video card in my opinion.
What do you have planned?

You're not supposed to turn your A/V off ever, but if you're only playing a game, aren't surfing around suspect websites, or aren't running any questionable software (which I doubt you are, seeing how you've been careful thusfar), the chances of you getting a virus are virtually 0 - especially if your firewall is running. Don't bother unplugging your internet connection.

Anyway, none of that matters because your computer is going to be able to handle pretty much everything you throw at it. The 7900gs is a good mid-level card. I think you will be very happy. There are a few games out there that you won't be able to run at high settings, but when you figure it'd cost an extra ~$800 to play at max settings, I suspect you'll find that it won't be worth it.

2GB of RAM is a ton.