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#11
I put install of 7 on an old XP case with a pair of 512mb ddr2 pc2700 333mhz dimms with one not working until removing it, cleaning the contacts, blasting dust out of the dimm slot, and then saw 1gb after 7 was installed. The basics will run while any large program will bog right down. Windows will overall run slower.
Vista would have run even slower and recently I advised one Vista laptop owner to replace the two 512mb sodimms that came with for a pair of 1gb modules. The owner noticed the improvement right away as well as the faster hard drive that went in as well.
A clean install of Windows will run faster without any hardware change simply by starting off all over again with a fresh system registry free of clutter as well as not having a ton of programs on creating a list of startup items to load the OS down. 7 will still run while the increase up from 1gb to 2gb will be noticeable.