Did you disable many of the services? Mine hogs like 950mb memory right after a start-up (Win7 64-bit Ultimate). Having said that, 60% at idle is no where near good also. 60% of 512mb is 307mb, so you're left with 205mb for personal use... even playing a flash-game in firefox would eat all what's left of that...
Read the repo. It says: "If you wonder which edition of Windows to install, be aware that according to Microsoft, all the editions of Windows have the same level of performance (system requirements are the same for all editions). Differences between editions are mainly about functionalities (compare editions of Windows). The Ultimate edition is the edition that includes functionalities from all the other editions, this is the most complete and the most extensible."