|Ah! I should have looked further down.|
In that case the OP should check his motherboard to see if it has 2 or 4 SATA ports. I suspect it has 4 as you rightly pointed out.
That to me suggests from the page I linked to that there is a 1TB limit per SATA port.
Thus he could in theory use 4 SATA drives of 1 TB each on each of the 4 SATA ports if he has space to accomodate additional drives..
The OP should however, contact Dell support and ask Dell to confirm the 1TB limit per SATA port.
I had a quick look on the Dell community forums and while I could not find a specific question about the 545MT , I found one about the 530. This one seems to suggest you can go higher. The 530 if anything is a lower spec then the the 545. Still the OP should confirm this with Dell or take the risk.
One additional suggestion would be to buy 1 SATA drive that is greater than 1TB and then try it. If it works well and good. If it does not then you can buy a SATA USB hard drive caddy and use it as an external drive.
☺ When everything else fails, read the instructions.