Is my Jeep ok to drive?

Hi,

I have a 98 Jeep Grand Cherokee, and I think the rear U Joints may be going.  I've already been told the front ones need changing, but the guy that was going to fix them said it was too rusted and he couldn't get them off.  Now, I'm concerned the rear ones are bad.  I'm not sure, but I keep hearing a kind of ping noise and a clunk when I let off the brakes from a stop to accelerate.  There are other issues with this Jeep, and as soon as I get my tax return I plan on purchasing a different vehicle.  I'm concerned though, because I've been reading online about when U Joints fail and the driveshaft could drop causing my Jeep to flip over.  I only have to drive it to an from school 2 days a week, which is about 20-30 miles round trip.  Based on that, I should only need to drive it about 12 more times before my tax return comes and I can purchase a different vehicle.  Does this sound like I will be ok taking it to and from school until then?

Thanks so much!