Okay, the basic version of the KT3 Ultra doesn't have the Promise RAID chip on it, but if it did and you wanted to use it right off the bat (before installing the OS) you'd need to feed XP drivers.
FYI: If you wanted to do that, you'd simply need to hit F6 at the beginning of the initial setup.
Anyway, you may be fine with snagging the cheapest, but you sometimes have a better chance of running into some problems by going the cheapest route.
If you need to save money now, you could always buy 256MB of something a bit higher in quality and pick up another 256MB later on. Right now, RAM prices are kinda high, so unless you absolutely have to have 512MB (and that's not a bad thing to have), I suggest paying for something other than the dirt cheapest stuff you can get: something like Samsung, Crucial/Micron, Infineon, or if you really want some good stuff, Corsair---which is the most expensive RAM you can buy, but I've yet to hear anyone bash it.
I personally like Samsung--and that's what's in my boxes with DDR. They have very solid memory, and I'd highly recommend them.
If you go the cheap route with that ad you're looking at, it looks like you get whatever they send you, which could be crap like PNY (I have not been impressed with their quality, or lackthereof), or some other brand of questionable quality. I've never had a problem using a quality name brand, but I have when I've tried some cheaper stuff before.
I'm not saying go buy the most expensive stuff you can, but I am saying that it'd be a better idea to go with less memory of a quality brand.
64 bucks for a 256MB stick of Samsung PC2700 DDR CAS 2.5 over @ Newegg
http://www.newegg.com/app/ViewProdu...147&manufactory=1077&DEPA=1&sortby=14&order=1
And it's free shipping.
Crucial also has some 256MB PC2700 CAS 2.5 sticks over at their site for 68 bucks with free shipping.