Hi Gerry,
The easiest (cheapest) way to do this would be to get an adapter cable and use the 3.5mm stereo output from the built in soundcard of your computer directly to the inputs of your Otari. You can pick up a 3.5mm to dual RCA cable from just about any electronics store (Best Buy, Radio Shack etc). If you have to use XLR inputs to your Otari, you can pick up RCA to XLR adapters at some place like Guitar Center.
If you want better sound and get the advantage of the higher sample/bit rates, the best thing to do is to process the digital signal outside of the computer with an outboard device via USB or Firewire. There's a gazillion choices but for around $200, E-Mu has some decent units.
http://www.emu.com/products/product.asp?category=610&subcategory=611&product=15185For price/performance, it's pretty tough to beat the 0404.
This stuff changes almost daily and I haven't really looked into what's out there now so it would be worth your while to do your homework on that. Just be sure that whatever you get is compatible with whatever type of computer you have and the operating system you use.