These are available on the secondhand market really cheap (mine were actually free), but there are a couple of caveats:

If you're shopping for these machines, get the "Simple Swap" disk configuration, not the "Hot Swap". The hot swap versions use an Adaptec AIC-9405W chip on the SAS/SATA controller that's unsupported.

The SATA RAID is actually Adaptec Firmware on the ICH9 chipset. It will look like a JBOD configuration, regardless of what you set up.

To convert a "Hot Swap" to "Simple Swap":
1. You need a pair of SATA Drives. I used 1TB Samsung 15K drives
2. Remove the top cover and the internal hard drives
3. Unplug the SAS cable from the Mini-PCI RAID Card and the disk backplane
4. The backplane will slid up and out. Disconnect the power cable now the board is free. disconnect it from the power and motherboard while you're there
5. Remove the Mini-PCI RAID Card (or just disable it in firmware, your call)
6. Slide the drives back in, the power and SATA connectors are now exposed.
7. There are two SATA power cables near the drives. These need to be turned upside down to connect to the drives. The left hand one is a bit of a stretch, but it does fit.
8. Connect SATA cables from the drives to the two SATA connectors on the left edge of the motherboard. Right-angle connectors are handy here.
9. Put the cover back on, set up as a JBOD in the RAID firmware
10. Boot from the ESXi 4.0.0 CD, install and admire your cleverness!

Thanks for posting your notes.

Dose this apply if you want to install esxi4 on one of the internal hdds or to use the interal hdds in general?

i have this U1 and its set up in sas mode, after opening the case i noticed these run though the raid card as u discussed but on the main board there are also two sata ports are these the ports that you are refering to (to connect 1tb drives)?

I want to run exi4 of a usb flash stick connected to the server and use the internal drives as vm storage, any suggestions?

Ta for any help