unless someone can chime in with a driver suggestion for that card, you may be back to the age old game of "Try a driver for a week, if it works, great, if it doesn't try another..."
However, be aware that the 3GB switch can have a negative impact on OS stability, even while having a positive impact on Revit stability. It is, to put it bluntly, a kludge. And at 1 GB of RAM I would expect that v4800 to perhaps never work with the 3GB switch. Basically what that switch does is give applications the impression they have their own 3 GB RAM playground. But it also tells Windows to play in a 1 GB playground (because in 32 bit Windows 4 GB of address space is all you get). Well, Windows also has to address video RAM, and that comes out of the 1 GB you have given Windows. And Windows needs at least 512 MB of that 1 GB for itself, and another 100 MB or so for the network card. Which when added to say 512 MB for video RAM addressing, puts you over the 1 GB that is left for Windows. Thus the old advice to never use a graphics card over 256 MB of RAM if you are using the 3GB switch. You can tweak the ratio a bit using the USERVA switch, but even that gets to be a huge amount of work trying to find the right settings, matched with the right driver, and the mix changes with a new build of Revit and you might have to start over. And when you don't have the right settings the result eventually is a crash and lost work. At some point you kinda give up the kludge and solve the actual problem. And if you are indeed working in models large enough that the 3GB switch is required (over 100 MB on disk and it starts becoming an issue), then the only real answer is to move to 64 bit Windows and Revit, and up your RAM to a more appropriate level. I know now is a bad time to be spending money, and a switch to 64 bit also means a switch to Windows 7, which is no small undertaking. BUT, if you are reaching the point where file size is consistently affecting stability there really is no other answer. Well, other than simply forcing yourselves to build smaller models, which is made harder with each new version of Revit. And hard because as people get better at Revit, the logical thing to do is to put more info in the model, which makes it bigger. I think it is much better to get good machines and let people work with fewer limitations.
Think of it this way. You have a kid who is a great driver. In fact, she is good enough to race. Sadly, she has outgrown the '76 Ford Pinto she learned in and it may be time to get a proper race car and turn her loose on the track. And putting a 600 HP Formula 1 engine in that Pinto probably won't actually result in a good, fast race car.
EDIT: I was just thinking, if these are new T1500 and they came with 32 bit Windows 7, then your upgrade path to Windows 7 x64 is much easier. Well worth considering if that is the case.