trying to upgrade my computer, what should i upgrade first, what will make the biggest difference.?

Don't know what kind of machine you have but generally memory is the cheapest and best upgrade you can make. Here is a link to a site that will analyze your PC and tell you what upgrades will work for you. http://www.crucial.com/

Sorry but not enough info to give you any exact advice.

Actual model number and what the machine specs are will get a better answer.

If you want games, you probably need a Graphics card first. If you have Vista Enterprise as the OS suggests it's an old Business Machine? Probably has no GPU installed, and that means you wont even be able to run older games.

An entry level GPU should be affordable, work in the older hardware and will let you play many of the older game titles.

More RAM may be useful, but you probably only have a 32 bit OS which restricts you to 3.something gb of ram.

To go further than that I would be looking at another ex lease business machine. Something with an i series CPU and Win7 64 bit licence. An cheap i5 with 4 gb of RAM and the low end GPU that you bought for your current machine is going to be a lot more use than maxing out the Pentium or Core 2 machine you have now.

If you want to play the latest games, you will need more modern hardware, basically an I5 with a good GPU ($)

You need to provide what you have first to make a recommendation. It might not even be worth upgrading at all so it depends.

How should we know? You failed to provide any useful information. How about you start with the make and EXACT model of the device, and list it's specs?

You can put a new memory coz it's very cheaper and your computer will be update after that.