Out of the question ... sorry.  The 2850 supports SCSI only, and SCSI is NOT compatible with SAS or SATA (adapters may exist but extremely unlikely one that would work with the chassis/backplane of a 2850, not to mention, it would be a waste of an SSD to put it in such a setup).  There is also no way to outfit a 2850 with a SAS backplane (even if you could find one that would fit, you would need to attach it to a different controller, plus the power to the backplane would probably be all wrong for it and the drives to work properly, if at all).  You would be better off getting a cheap 2950 (if not a new server).  You can go to 300GB SCSI drives (if not already at that size).
Hey Everyone,  I'm trying to save time by asking the experts.  We have a PE2850 and were wondering if we could swap the current scsi drives with SSD drive? The idea being just clone what we have and image the new SSD drives. We just need more capacity and the drives have a lot of spin time. Any ideas - suggestions would be greatly appreciated. 
Replace drives with SSD drives?