You can reassign the partion to something else. But one thing to consider is if you do ever exceed your RAM it will make your system crash.
So to reassign it,
1) In fstab comment out the line for the swap partion by putting a # at the begining.
2) then either reboot or run swapoff.
3) Now lets put /tmp there. You should change to runlevel 1, this will stop most services on your system and leave you with a minimal system. It will also stop X, so you will be doing everything else from the command line.
4) On an ideal system /tmp should get cleared out on shutdown. But if for some reason you have something that you want to keep now is the time to put it else where. If there is anything left you should delete it otherwise you will just be wasting space.
5) Now in fstab we need to create the line to mount the partion. which will be,
/dev/hdaX /tmp FS defaults 1 2
replace X with your partion number and FS with the filesysem type.
6) Next it needs a filesysem. You can use which ever you prefer but for this example we will do it in ext2. So run mkfs.ext2 /dev/hdaX (replace X with the partion number, and in fstab the FS will be ext2). And this will create the filesystem.
7) Now all that is left is to mount it with mount /tmp