80GB. Only install OS and Programs to it.
Get a second (or your current) hard drive for data/media.
Only use 75-80% of the drive, so the drive can self-optimize. That would be 64GB, plenty for Windows 7, and Office...etc. How much space do you currently use?
Partion the drive (during Windows install), using 64GB as primary partion, leaving 16GB unpartioned and unallocated. Read other posts about this, there is alot. If using Windows 7, let it partion 100MB as "System Reserved", and continue with 64 & 16+/-.
Okay?