There is no easy way around this but to rebuild the RAID array. Here are a few comments that might help to reduce your RISK of downtime /dataloss.
o) I like to have an online copy just in case. Map any critical network shares from any other computer that has sufficient diskspace & SCOPY ( in the resource kit, to maintain security & ACLs ) the files to it.
o) Perform a backup & test restore a few files. You should be doing this anyway if you are not happy with the backups, to build confidience / experience.
o) If you are worried about the data/services being offered then you should seriously look at being able to restore your backups. Backup Exec have an Intelligent Disaster Recovery (IDR) that I have used sucessfully. It still takes a bit of practice & confidence.
o) Make sure you have more than one backup of the server & make sure they are backed up with VERIFY. Its a good habit to WRITE PROTECT the backup tape you are about to restore.
o) Good practice is to be able to backup the server & restore to another computer. If it is exactly the same it is a lot easier, but if not you may just have to worry about the ethernet & HDD controller drivers. This is brilliant if you expect lots of downtime during reconfig or to be able to work on business recovery
o) Its always a good Idea to have a seperate system partition/disk array to a data disk array. You can minimise the abount of data to be horsed about.
0) If you are adding the extra disk for addational storage, why not add two & mirror them ( or three & raid 5 them) , you can then use this extra diskspace without any backup/restore. It will cost a bit more but if you can fit it it may permit you to defer the rebuild of the raid for a while.