12345 said:
Its says that 512 is not good for windows 7 but my gaphics card is supported by windows 7 and my graphics adapter does not support windows aero
I suggest that you read this:

 Older Intel® Graphics Controllers and Microsoft Windows 7*

Intel hasn't made Windows 7 drivers for some of their onboard graphics, including yours. XP drivers are the latest. They may be made to work, but Aero Glass effects will not be available.

If you desperately wanted Aero, you could add a graphics card that supported it. From the specs of your Dimension 3100, it would have to be a PCI card or a PCI-Express X1 graphics card. Most graphics cards are PCI-E X16. I wasn't sure whether PCI-E X1 graphics cards existed, but www.newegg.com lists a few (based on the ATI Radeon 4350 chipset). There's a little more variety (and lower prices) in the plain old PCI category, although PCI-E (even X1) may give better data transfer rates. (I don't know the specs.)

I would have suggested staying with XP for the remainder of the useful life of this PC.