Your best bet is to tighten it to about the same tension as the spokes immediately surrounding it. If you have brake blocks spin the wheel and check if it's straight.
If it is not straight, you have two options.
1) Take the wheel to the LBS and have them true it. Since your spokes are coming loose, it's a clear sign that the wheel is not tensioned correctly. You should ask them to tension it while they're at it. The correct amount of tension is the maximum that can be applied without rounding the nipples.
2) Dive into the wonderful world of wheel truing and be prepared to make a LOT of mistakes. The road is long but ultimately very rewarding as you don't have to wait for the LBS to finish your bike. Don't cry for the LBS. There is an unlimited supply of persons who cannot work a wheel from lack of time/patience and others that lack ... well ... they don't learn so well.
Last edited by willtsmith_nwi; 08-29-06 at 11:21 AM.