the only reason why people say 7 isn't as good as xp is because of the hardware requirements, in which case a good dual core processor and a decent enough video card along with 2gb of system memory will run windows 7 without any problems.
another thing is compatibility which has improved quite a bit almost any program you can run on xp with the above mentioned setup you can run on windows 7 and the only reason for the almost is the compatibility in some cases between older 32 bit programs on 64 bit windows 7.
also the memory management has improved from vista to 7, where as in vista when it first loads up at 500+mb of memory it stays when you run a cpu or memory intensive program while on 7 the same situation takes the memory from programs that aren't utilizing as much cpu or memory and puts the usage to the program that requires it the most at that moment.
windows 7 has the performance of windows xp pretty much along with newer enhancements such as directx 10/10.1/11.
for older computers though windows xp is the way to go.