Personally, and this is ONLY my opinion, so please don't anyone flame me, I think prices are good right now for the regular 266 FSB 1.4 GHz AMD T-Birds. If you want the upgrade now, go for it. There will not be a big difference between "regular" and "AMD 4" T-birds for a single processor user. If you do wait, however, then the price of the "regular" flavor may drop even more.
Regarding the case, make sure that it will accomodate both an intake fan in the front and an exhaust fan in the back just behind the Socket and HSF. That way, you get good air circulation and the hot air will go out the back of the case more efficiently. I personally like the "screwless" cases where the drives and such simply snap in, but as long as the edges are all rounded so you don't cut yourself and you have good cooling, any case should work. You have to look at space restrictions, too, because some people only have room for a mini or mid tower, while others can go with a full tower. My other suggestion would be that if it comes with a power supply, I would try to get a 400W power supply so you can power that chip and all of the other hardware you will be decking in out with.
Again, just my $.02. If someone has other advice, please don't jump me because my opinion may be different. Thx.