i always unplug cable modem first because i always install my firewall first,you will find it easier this way you can load norton etc first,i left it in once and got blaster virus before i had finished install.i dont know a great deal about partitions but they are used to store seperate files,games,users,and operating systems etc,also they make defragging,manageging or copying of portions rather the whole hard drive easier.hpoe this helps
to your partition question, it depends what your gonna use each partition for really. i tried it and thought it be good, but you really need to think how much disk space you wanna give for each partition.
i have a 80Gb drive and i thought i parttion it into 4 drives, and thought 10Gb would be enough for Programmes, and the rest for work, films and etc
when you install programmes, bits of files will be placed into the C drve all the time, it doesnt matter if you chose to install on partition drive E, it still will save bits of files to C.
i didnt really like it so i had to put the partition back to make the one drive again (use Partition Magic if you wanna go back to one drive) and that took ages to reinstall, and install XP back in.
i rather just do a RAID config, or just buy another hard drive and use it in the machine, its saver and its better to store seperate things on each making whichever drive you use faster and less of the junk in one place.