well, it depends on everyones need... as far as um concerned i have made 2 partitions of my 45GB hdd one primary dos partition of 50% and other extended partition of 50% (all 50% assigned to 1 logical drive)
here is info about my drives
Drive C: 18GB (18GB IBM , i have made only 1 partition)
Drive D: 22GB (50% of 45GB)
Drive E: 22GB (remaining 50% of 45GB)
(windows detects my hdd as 44GB, its normal coz WD consider 1000KB as 1MB, but its 1024KB=1MB)
i dont really like making more than 2 partitions of single drive
I would go with kashi80's suggestion. if you have at least two partitions you will have a drive to save things to in case you ever have to reload the OS. I partitioned my 30GB drive into two equil sized partitions and am real glad I did.