Need to swap hard drive in Raid 5 array

We have an HP Netserver LC200 running Microsoft SQL Server 7.0 on it. It has 5 9GB Hard drives. 2 drives are Raid 1 mirrored and 3 drives are at Raid Level 5 in an array. One of the 3 drives in the array needs to be replaced. Normally this wouldbe easy to swap with another 9 GB, but we need to swap with an 18GB drive. I need to do this without losing any data. Rebuild the drive and restore all data. I need a solid plan of action. Anybody with an expert opinion???