First of all, this may not be the best forum in the world to ask such a question (just read some of the other lame "funny" replies) but since you asked, I'm assuming you're looking for an answer from someone who actually works with this things on a daily basis and will be able to provide some insight.
The hardware on the computer does have to meet certain requirements but they're not really "set in stone". At my work, we typically use off-the-shelf Dell computers and then do some modifications to support removable hard drives on the systems. Additionally, you'll probably need to lock down all writeable removable media drives (think floppy and zip drive locks) as well as disabling USB and any built-in network interfaces, at least in the BIOS but possibly also with some stickers or physical locking devices. You'll have to work with your DIS person who approves the final system configuration to really hammer out the details and get it set the way he/she wants it to be set.
That being said, the only service I've seen Dell offer is their "Custom Factory Integration" program where they will install the removable hard drive chassis for you. Depending on the number of systems you need to support, it may be cheaper to have them do it at the factory than to do it yourself. One issue I had which caused us to do the removable drive install ourselves was the fact that we have multiple drives per system and needed extra drive trays but couldn't get information from Dell regarding the actual manufacturer of the trays nor pricing on additional units. It was just less hassle for us to purchase the removable kits ourselves.
As far as software, I believe another poster already mentioned some of the basic configuration requirements. Yes, you'll need to make sure you're pretty good on locking down Windows (I'm assuming your running Windows since you mentioned SolidWorks - BTW, SW2006 sucks configuring it to run with a non-admin user account). Auditing on certain directories is most likely going to be a requirement as well as a documented review and archive process for the system event logs. Backups are another process that will need to be done on a regular basis. Be prepared for this to eat into alot of your time since all these tasks pretty much have to be done manually since you can't have network connectivity.
If you've got any more questions, feel free to drop me an e-mail and I'll try to help you work through any issues. And don't mind any of the other sarcastic bastards posting here... I've seen the level of documentation the government gives for setting up secure systems and most of it is pretty f'ing obtuse. Best to get advice from someone who's done it before (and obviously double-check with your FSO and DIS officer).
Best of luck...