[OnBoard]

Yep, HDD will be the botteneck always and buying a fast sata drive would help with that a bit. Keep the old for storage & games, if you don't mind slower loading times. But the start of HDD (outer edge of the disk) is always fastest so first partition should be swap partition then Windows/application partition and rest for rest. If you want to maximize the speed of what you got.

Ideally if you get a new HDD you make a 4,5GB partion for it and place 4GB swap file there (Windows complaints if there isn't 10% space free). Then cut the rest of the space in half and make a partition for your games/programs that need fast startup and use last partition for storage. Keep Windows in the old HDD and use rest of the space of it as you wish.

Swap and Windows shouldn't be on same partition/disk for best performance. Above is what I use, although my swap partition is only 1GB, because I used that in XP with 2GB mem. Didn't have space to store all my junk to re-partition, so it'll have to do with another 3GB swap on another HDD.

edit: forgot, after that you can change drive letters in disk management, S: is a nice drive letter for swap partition or P: if yo like Page File term better. Although you have to change swap partition drive letter before it has the swap. Or leave them be if you don't mind the order of the drives.