This may not answer your question, but the WL-138g is a horrible network card from my experience. It was a big pain to set up and use the way I wanted to. In the end, I'm now not using ASUS drivers at all but drivers directly from Marvell found through device manager's update feature...
I don't know about it not being detected--that's a tricky one. Didn't the card come with a CD? Try downloading the drivers and using them and see if anything's detected. If it's not, try a different card. There really is no hope for this one in terms of improved features or any of that. It has worked alright for me lately, but I am using a third-party wireless program (Odyssey Client) to keep stability. I'm not sure if the stability problem is that of the card or the router (probably the router) but still... I'd get a card more well-known, probably one with afterburner support too, but that's not completely necessary
My advice may be the best you'll get when it comes to this card . Sorry about that. Just warning you--don't keep it if you still can get a different one. I wouldn't wait around for a reply here.