I would do the RAM upgrade first. The drivers are probably not what is causing the slow down. Check for spyware. Keep from launching any not necessary programs on startup. Set the visuals to maximize performance. Do not let Windows decide or adjust for best appearance. That stuff eats up performance. Also, if you can afford it, go to Windows 7. One little known change is that 7 handles video somewhat better than Vista.
Probably Can go to Windows 7 on Mom's PC, do have Extra upgrade Copy of WIndows 7 (Retail) that was used on my older out of commission Desktop...(New one is OEM Windows 7 64bit, soon to be WIndows 8 Pro for this machine)
Ram upgrade for Mom's PC will be done soon as i can afford to buy the memory, then it's fun task of getting to the memory slots in that Slimline HP PC lol
Except HP doesn't have Windows 7 Drivers for that model PC, Only Vista 32bit or 64bit
There is some risk but most of the Vista drivers work in 7. I would get one of those restore CDs that HP or MS should be willing to supply to get back to Vista if it all goes crazy after going to 7. HP Slimline! Our IT guys dislike working on them as much as they dislike working on HP laptops. Too much is too easily broken. Those things really do need surgeon steady and sensitive hands.