You are good to go! I am hoping you have more than 1 hard disk, though.
There is no need to install drivers. In fact, you couldn't even if you wanted to. All of the drivers are built into unRAID's version of Slackware.
Here is a high level list of the steps you should follow ...
1 - Put the machine together. Take your time. Make sure that your cabling to your drives is secure. Do not use mangled cables or ones that have caused you problems in the past. Factory fresh cables are recommended.
2 - Double check all connections.
3. Then boot the machine and make sure all of the drives are recognized by the BIOS and/or add on controllers.
4 - Get your USB stick formatted and the unRAID distribution files installed. It should create a subdirectory structure. If all of the files are on the root you didn't unzip the contents right.
5 - Power down the server, install the USB stick, reboot, go into BIOS settings (usually pressing DELETE), and configure it to be the boot device (this is motherboard specific configuration - post if you have questions and someone with that MB may be able to help). On my motherboard I was able to configure the USB as a "forced FDD", and configure the motherboard to boot off of that as a removable drive. Again, the Supermicro BIOS settings may be similar or totally different.
6 - Confirm you can boot off of the USB stick - you should get a boot menu with 2 choices - unRAID and memtst.
7 - Boot into memtest and let it run for 2 cycles. Later you might want to come back and run it over night, but 2 cycles should give you pretty good confidence that you don't have a memory error.
8 - Press ESC to reboot, this time go into unRAID
9 - Run Joe L.'s preclear script on each of your drives. (Several of these can be run in parallel, as these tests take time). Although pre-clearing the drives won't help you, this script really runs the drives through their paces, and if they have any SMART errors they will likely get detected before you put them in your array. (Although recommended, you don't have to do this step in order to proceed to step 10).
10 - Configure your array
You may want to hold off assigning parity if you have a lot of data to copy over. I'd suggest copying it with no parity installed, but that you install and build parity before you delete backups of anything you put on the array.
11 - Start the array
12 - Copy your data from your workstations / existing servers to an array disk.
13 - Install your parity disk (if you haven't already)
14 - Start unRAID and let it build parity
15 - Run a manual parity check - make sure it completes with 0 sync errors
16 - Run smartctl on each drive to make sure that no serious errors have developed. Post them as well as a syslog and a forum member can help make sure there are no errors to be concerned about.
17 - Only then can you delete backup data and think about moving existing data disks from other machines into your unRAID box
Post back if you have any troubles and I'll try to help.