Very nice windows 7 theme for those interested;
http://ap-graphik.deviantart.com/art/Soft7-2-0-BETA-1-161602097
http://ap-graphik.deviantart.com/art/Soft7-2-0-BETA-1-161602097
I've been using custom themes, patches, dlls since vista. Never had a problem. Maybe you've been unlucky.I used to play around with XPize in XP, but I wouldn't touch these with a barge pole in Vista/7, since files that Windows update replaces are archived within Windows.
You could be opening up a plethora of problems for the future.
Performance 'tweaks' and bitmap patches like these should not be used in Vista / 7