URGENT - Backup Hanging

My overnight backups hang occasionally. I say this because there is no consistancy to when the routine will hang. It happens on the first step where it reindexes. The only user database on the server is about 12GB. The server is dedicated to SQL so nothing else runs on it. It has 2x 800 MHz processors with 2 G of ram of which 1.5 is allocated to SQL.

I can't trace the error because it happens before the report is written to. There are a few tables with a million plus records that take up almost a 1G per table.

It was my understanding that if users were in the database they would notice a big performance loss but that the backups would still run. Could it dying because of resource contention? I'm at a loss and really could use some input. I can't afford to go a whole weekend without a backup.

Is there a way for me to progammatically check who is the database prior to the job kicking off?

Any ideas as to what would cause an inconsistant hang of job is greatly appreicated.

Thanks,
Kelsey