it really depends what you want to do, what you feel most suited to etc...
personally with that space i'd go with something like:
c: OS 4gb
d: programs / Program Files 50gb
e: files / My Documents 50gb
f: backup 10gb
g: swapfile 1gb
f: is used for the most recent ghost of C:, temporarily holding downloaded files until burnt to cd/dvd, occasionally holding a backup .rar of My Documents until burnt to cd/dvd... if having a second hdd, f: and g: most likely to be going on it, then e:. This approach seems convenient -- to me! -- for occasional complete backup of the OS for easy + quick "reformat reinstall" that doesnt screw up program's registry entries etc. Personal files are kept seperate in whatever way you want to organise them, also allowing for relatively easy backup... backups have their own space to make frequent temp backups and more occasional proper backup onto cd or dvd. swapfile kept seperate to reduce fragmentation (if onto a second hdd, a minor performance increase also).
As you can probably see though, it really comes down to preference. I put quite a bit of consideration for ghosting the OS because i like to fiddle and customise a lot, and also for downloads/files etc as i have a slow 64k isdn.
Useful programs, IIRC - Norton Ghost 2003 for ghosting entire partitions, useful for being able to completely reinstall it to exactly how it was when you made the ghost. MS Powertoys/TweakUI to change window's idea about the default path to Program Files and My Documents.