I agree with colbec on using a regular STB receiver and slaving the PC off it. That will be much easier to get setup. I would suggest the Coolsat 6000 myself.
You'll be able to move the dish reliably with the STB and get familiar with the PC software. Once you're comfortable with the PC software you could leave the STB in standby and use the PC software to move. USALS support is more about the software than the hardware on PC cards I believe. Since the USALS "Goto X" message is just sent via the DiSEqC encoder on the board.
The question is do you want just DVB-S/QPSK or do you want DVB-S2/8PSK also? I use a Twinhan 1020a for DVB-S and a TBS 8920 for DBS-S2. I just recently got the TBS 8920 so I haven't used it much yet, except with TSReader. I use my STB to move the dish.
I would suggest figuring out what software you're going to run and find out how well it supports USALS and then what cards work best. Of course I suggest getting a card that works with TSReader.
The TBS 8920 works with TSReader *via* DVBDream tuning the card. It is a little bit clunky, but works. I have not tried using USALS under DVBDream to move the dish, but expect I will eventually.