Yes, it is worth it. I didn't mean for you to get the idea that it wasn't.
The more video memory in a video card, the faster it'll run games. Well, the more information it can hold in a given moment so it can process things faster by storing more information in a given moment... if that makes sense.
The higher the clock speeds are, the faster the card'll run. Clock speeds are like speeds for a car; the higher the top speed is, the faster it'll go!
I'm not really an expert on video cards and how they work (well... come to think of it I'm not really an expert on anything computer related...) but I'm trying my best to explain what I know...
Here's the choice it really all boils down to. If you want to be able to play games, you're not going to want that X600 SE in your system very long. You could buy the Dell, then upgrade the video card right off the bat to something that suits you better. That's option one.
And I still keep coming back to this thought: build your own system! You can get exactly what you want and then learn how everything is constructed and know how to troubleshoot your own computer. Trust me, it really isn't as hard as it looks! When I first got my Asus motherboard, I dreaded opening the instruction manual figuring they'd surely forgotten to throw English into the languages it had. Actually, the manual was very helpful and well-written, which I was pleasantly surprised with. It had quite a good amount of information as well as troubleshooting options.
Here's another quick thought. If you buy the Dell, you'll still be able to use your other system. If you build your own computer, you can use the old drives you had in your other computer instead of buying new ones (unless you want to upgrade that too). If you wanted, you could just keep your 40 GB hard drive instead of getting a new one to save money. Now, keep in mind, though, when you undergo a change in motherboards, Windows will not start. You need to get all of your important files on CD's, DVD's, or on a FlashDrive or external hard drive before you put the hard drive into the new computer. Also, you should download a program off the Internet that will completely reformat your hard drive (such as KillDisk) before installing Windows again in the new system (though Windows can reformat the drive for you as well, I prefer using KillDisk because it is more thorough and I've had problems with Windows reformatting my drives before).
Well, that should give you something else to think about for a few
. Hope it helps.