If you're using FAT32 (I assume for compatability with older OS) then avoid partitions bigger than 32.0GB, if using NTFS use any partition size. FAT32 is very wasteful, try to stay near AND UNDER the limits of each cluster size (eg 8GB, 16GB, 32GB). Only downsides of NTFS are poor compatability with older OS and it fragments more easily (because it is more economical).
From what most people advise you'd ideally want the first partition (OS) to be pretty small (16GB?). If you want some room for your Internet cache, temp folders and swapfile then 4-8GB is plenty. To set your swapfile up simply set a minimum size under the 'System Properties' (r.click my computer), Advanced, Perf, 256-512MB is probably best but do leave the maximum size alone as this should automaticly be the full amount of free space. You'll have to untick the other partitioons or drives manually if you don't want them included.
Doing all this will hardly give you a noticable effect (apart from setting a minimum swapfile size), it's always better to have a 2nd HD for temp folders, swapfile etc and certainly for dual booting. I personally hate partitions and don't think they're relevant any more but to each his/her won. Whatever you do, defrag and scandisk regularly.
If you want your boot letter for Windows to be D: you can plug in a harddisk on Primary then tell Windows to install on the HD attached to Secondary. Otherwise you could try things like installing on an extended partition or creating 2 Primary partns (WinXP handles this well). HTH.