I am experiencing exactly the same copy and paste problem on my HP Pavilion Slimline s7700n with Vista Home Premium with very similar specs. Even copying 21 KB from one C:\ directory to another just took me about 40 seconds.
My Windows Explorer is not intolerably slow, except when trying to read from CDs. I backed up some pictures from my old XP PC, and trying to view them on the CD is so slow that it usually locks up Windows Explorer. Each time is locks up, it takes literally about 3-4 minutes to recover (much longer than even on my old XP machine).
I could probably accept this if I knew it were a known issue. Until I saw this thread, I assumed there was something wrong with my particular PC. If anyone is familiar with the issues above, I would be settled to know that it's Vista that sucks and not me. Thanks!