I've just upgraded my computer I brought from Mesh. I rang up their customer service number, which is on their website and they were very helpful. They knew what computer I had and I was able to upgrade successfully as they advised me what to do.
I agree you shoudl give mesh a call ad see what they say about your system if you're not sure about the minimum specs. Vista is beast that eats resources for dinner - best amke sure before you install.