Windows 7: Recommended free space + diff btwn H-Premium + Ultimate

I have an Asus EEE 1000 which has an 8GB primary SSD and a 32GB SDHC as a secondary drive.

After installing Windows 7 Ultimate 32bit, installing all required drivers and getting all the Windows 7 updates I am left with 475MB. All programs have been put on the D drive, system restore has been completely turned off, along with hibernation and the page file has been moved to D and Ccleaner is used regularly. In Windows services, tablet PC components and Windows DVD maker have both been removed but from what I’ve read online that is about all that can be easily/safely removed/moved on Windows 7.

My questions are, what is the recommended free space that there should be on C? On XP, I was always told you should have 15% minimum free space.

Second Q, what is the installation footprint of Home Premium compared to Ultimate? I used Ultimate because I had a copy but if Ultimate uses a shed load more space Home Premium might make more sense.

Thanks.

there should be a special windows version for small hard drive machines, stripped from many option that the regular user does not use, only takes up a few gb, i don't know what it's called, but heard about it from a friend that had the same problem.