Yes, it certainly sounds like low refrigerant. Most common place for a leak is the shaft seal on the compressor. If this is the original a/c, be advised that all a/c systems leak over extended periods of time (in my experience), especially if you don't use it, that's why you should run the a/c a few times a month even in cold climates to keep the seals from drying out.
If you're handy, it's a fairly straightforward process to fix the a/c, again I'm guessing it's the compressor that's leaking, you'll need a new one, as well as a new accumulator. If this is the original refrigerant (R12), those should be the only things you need, and once they're installed you can flush, pull a vacuum to -29 and re-charge with R12. If you want to retrofit to the new R134a, it's a perfect time to do it (if it hasn't been already), you'll need R134a-compatible o-rings too.
There are lots of helpful a/c people at this forum, why not visit:
http://www.aircondition.com/wwwboard/
also this is a great site:
http://www.diynet.com/diy/ab_auto_air_conditioning/article/0,2021,DIY_13674_2276708,00.html
If you are handy with tools and can follow directions, there is no reason to pay through the nose for a new a/c system from a mechanic. The number one tool you will need is a set of manifold pressure gauges, which you can buy off ebay for $40, and this will tell you the high and low pressures of the system. Secondly you'll need to buy or rent a vacuum pump.
