Hey OG - the 512MB of memory concerns me, but we'll see if we can get you off to a good start.
I tried a few programs (winamp is dead by the way - no longer developed or supported), and most were just big hogs trying to do too much. Which is no good with your limited memory. I finally settled on Foobar2000, which is a freeware software. It can be a bit...PC like of a software...lots of menus and sub-menus, and clicking and all that is having full access to a PC. That said, it only took me 10 minutes to get it going following a guide I found online that wasn't exactly like my setup, but close enough for me to figure it out and get it up and running.
Doing a quick search, I came up with this guide for you:
http://www.makeuseof.com/tag/play-music-audiophile-foobar2000-windows/You'll also need a source of files. I took my whole 1300+ CD collection and ripped them using dbPoweramp, which I don't believe is a freeware program, but it's fast and easy. It literally took me 3 months ripping a few CDs a night while watching TV to get through all 1300+ CDs. I'd recommend you rip to FLAC format for now - keep it simple. I'd get the software setup, Rip a few of your CDs to FLAC, and see if you like the computer rout before going whole hog like I did.
A couple things to keep in mind. Part of what makes Foobar a great program is it's simplicity. But you can add on features with "components" - these are little...lets call them apps, that programmers come up with that add features to Foobar.
Also, you need to setup Foobar to output what your DAC is capable of. For example, mine is capable of 24bit 384kHz playback, but yours might only be able to handle 24 96kHz (for example), and your playback software should be setup appropriately (though I try to avoid any downsampling or converting if possible).
For hardware, get a good, short USB cable. If you have to buy one, just get a $20 Belkin USB certified one from your computer store. Otherwise most any USB cable will do to get you started - just be aware they don't all work well with DACs.
That's all I can think off of the top of my head right now. Hopefully that gets you started.
I'm in Bolingbrook by the way - I (re)build and sell inexpensive laptops and desktops if you want something a little more powerful. I have a few that are pretty well good to go for only $150 if you find your current one is lacking. I'd be happy to have you over for a listen of my setup and possibly help you out with your current machine if you really get stuck.