Unsure what you mean by "cannot enter my past years of TT and Tax Cut". I just abandoned an XP PC and bought a new PC with Win7 64bit Home Premium. I have installed TT 2010 Dlx and TT2009 Dlx from the original TT CDs/downloads with no problem. (Well, I shouldn't say that - TT2009 gives me a problem creating a .pdf copy of the return, but no big deal.)
Had to buy TT2010 on eBay for $9 because I lost my CD.
I copied the TT data files (the ones ending in .tax2010 and .tax2009) to the new computer. Then fired up TT and did File|Open Tax Return and pointed it to where I had put the TT data files and everything worked fine.
Are you by chance trying to copy the TT and Tax Cut programs over from your old XP PC? That will not work. The programs have to be installed.