I am looking to buy a server with a 9gb hard drive so I need to to upgrade. Here is what the spec sheet says.

==============
SCSI hard-disk drives two 1-inch high slots in hard-disk drive bay support formatted capacities from 9 GB to 18 GB and higher

SCSI devices an Adaptec 29160LP Ultra3 SCSI card
==============

I was looking around at SCSI hard drives and I am totally confused. There are 6 or 7 different types of SCSI drives. It seems that the Ultra3 standard is the latest and greatest but they cost almost half of what the whole server is going to cast me.

So my question is, what type of SCSI drive will work with the above card. The drive bays are hot swappable, 80pin 1inch high. Will drives like the Ultra, 160 or Ultra2 work too? or does it have to be an Ultra3 drive no matter what?

SCSI is up- and downwards :) compatible

You may want to look at this for clarifications regarding SCSI technology.

http://www.pcinsight.com/articles/hddguide/hdd2.asp

SCSI-3 is the latest flavor of SCSI, but there are three different types of interfaces (HDV, LVD, SE) using SCSI-3. Different cards support different interfaces and require different cables. Make sure that the card and the drives you are choosing will match without having to buy adaptors. SCSI adpators can be expensive (>$50). If you are buying this as a pre-configured system, then you should be okay.

Well the bays are hot swapable and tell told me to find a drive thet had 80pins 1 inch high so there will actually be no cables.

So is there a difference between Ultra3 and SCSI-3 or are they the same thing?

Ultra3 should be called Ultra160 or SCSI-3. Make sure you get the right tight of 80PIN drive. There are standard and SCA interfaces. Many hot-swappable systems use the SCA interface which integrates power and drive connections into one interface versus separate power/drive connectors.

You need to find out if you need regular 80PIN connectors or SCA connectors.

After that, you may want to check out:
http://www.pricewatch.com
They have a great listing of prices

We just replaced two of our drives with Western Digital 18.2GB Ultra160, 10K RPM, 2MB Cache for ~$150 each.

Well I called dell to ask and their response was that it's 80pin and thats what they know. I guess I'll just have to figure it out on my own when it gets here....