Getting the drivers you need is a relatively simple process for most cases, although there are often those awkward ones that seem impossible, but there are a few things we need to do, well get you to do that is, to begin we need to know the system details, so if you have any make\model info that would be great, you've already said your using xp so thats fine.
Now to identify missing drivers click on Start - Control Panel - System (double click) - Hardware (tab at top) - Device Manager (button part way down), this will display a list of hardware, anything that shows with an exclamation mark requires attention, so note what shows and we can get all the drivers you need so your fully functional.
Now I am a little concerned over the licence, was this bought as a working system ready to go ?
I appreciate you say you had to install it, but was it sold as having an operating system ?
You say they gave you a licence, thats fine in itself, BUT, did they give you the sticker ? or is there a sticker on the case already with the licence ?
What I am worried about is that they may of given you an unofficial licence, the licence is the sticker itself, the OS disk is not what you buy, you buy the sticker as thats what gives you legal ownership, I just want to make sure you get a legit OS thats all.
Should you have problems in identifying the hardware inside the system, get and run
Everest, it will tell you everything you have in your system, and from that you can go to the makers site of each part that needs a driver and download the latest, you can create a report to post here if you don't understand what you see, BUT, if you do please remove the licence entry BEFORE you post it, just read down the list and you will see it not too far down, just delete that entry so it keeps it private, NO ONE has need of that code as that is yours (assuming it's a legit code), and the last thing you want to do is give that out on the net, hope this helps a bit anyway.