Windows 7 (and xp tablet edition) harddrive space requirements

im looking into a tablet with a ssd and the option of xp home(but id upgrade to tablet edition) or windows 7. the ssd that is included is either a 16gb or a 32gb. my question is how much actual space is really needed to install these OS'. i know w7 needs 15gb for 32bit but does it really need all 15gb? because then a 16gb would only fit the OS and nothing else

If you want to run Windows 7 on your PC, here's what it takes:
■1 gigahertz (GHz) or faster 32-bit (x86) or 64-bit (x64) processor
■1 gigabyte (GB) RAM (32-bit) or 2 GB RAM (64-bit)
■16 GB available hard disk space (32-bit) or 20 GB (64-bit)
■DirectX 9 graphics device with WDDM 1.0 or higher driver

this is from microsofts website..

i wouldnt plan on using 64bit just because the tablet i want can only get 2gb of ram and i can get a free copy of 32bit. if 7gb is all the OS takes up then i should have no problem. i plan on running a 32gb ssd with a 32gb + 16gb sdhc's. i just feared the OS would take up the entire ssd if i chose the 16gb ssd