Rob,
First question is what Generation DL380 or DL320 are you using? If it is a DL380 G1 or a DL320 G1, the PCI-Fast8 will work. The G1's have 64-bit/33Mhz (5v slot) PCI slots.
On the other hand if it is a DL380 G2, DL380 G3, or a DL320 G2 it will not work. Those servers have the PCI-X which uses the Universal PCI slot (also known as 64-bit/66Mhz or 3.3v slot).
If you are going to use a G2 or G3 take a look at the Digi AccelePort Xp. I have one in a DL360G2 (I went through 4 cards before I found one that fit)
Hope this has helped,
Ben