Small Business Server 4.5 FIle System Li

We are running Small Business Server 4.5 and are running out of disk space on one of the partitions. The partition that is running out of space is a little over 4GB and the Exchange priv.edb uses all but 100MB. We want to purchase a new hard drivebut the question is will that help. I know some operating systems have a limit on the size of a partition. Does SBS uses NTFS and how big can a partition be? Thanks.