Hmm..no more help? 
Naah...Just gettin in from work...LOL
a. How does one do the part in bold.
If you have a restore disk, its easy...usually most of your main software will be loaded on the disk and it will walk you through the format and reload. You may have to install drivers for certain devices and a few other software programs that came with your system, but all the disk should be there to get you back to a fresh install if you kept everything. NOTE: Make sure you back up your personal files you saved that you want to keep, (ie ".pst"-mail files, favorites, etc.,)
b. I just downloaded, what I believe to be, a newer version of SPYBOT (S&D 1.5.2.20). Can I get rid of the "old" or do they work in tandem?
I'm not familiar with these programs, I normally use BlackIce, Norton, HistoryKill...and I never use the free versions of any anti-virus/spiware/adware software...they usually don't have everything you need. Anyway, always make sure you have the latest versions/patch...If it is a patch to the freeware program, then yes you need the freeware program installed.
c. I also have, what I believe to be, two versions of AVG (Free Edition, and Anti-Spyware 7.5). Do they work in tandem or can I eliminate one of them?
Same applies here as in "b."