You won't be able to move the paging file to a external because it would need to be plugged in always to allow the file to work. That is why it says you can't use it.
2 gigs of memory OK now we are getting somewhere. Is your OS a 32 or 64 bit version?
Also do you know the total memory that can be installed on your motherboard and if not do the following.
Go to HERE and run the Crucial online scanner.
This will give you the exact memory configuration for your system.
You do not have to buy the memory from there, but write down the information and if you need assistance in purchasing the upgrade memory GTG can assist with suggestions also.