This is probably a better topic for the Operating Systems and Software forum, but I you might get better performance from your Access database with RAID 0. I would be surprised if it were drastic improvement though if you've already got reasonably good single drives (7200 RPM SATA or even IDE). There's some faster 10,000 RPM SATA drives you could look into as well if your system supports SATA drives. You might also consider SCSI, but that's pretty expensive. RAID 1 (on most newer cards and motherboards) will give you improved read performance (similar to RAID 0), but nearly the same or slightly slower write performance than a single drive. The advantage to RAID 1 is that since it writes the same data to both drives, you don't loose any data if one of the pair goes down.
Access can be a memory hog, too, so adding memory might have more effect. I'll assume you've already done whatever optimization you can inside of Access (adding indexes, etc.) (I don't work with Access databases that much, so I'm not familiar with what it offers in the way of tuning.)