If you are doing general office work and web surfing then ANY of these machines should be fine, even for the long haul. My Mom is still using a Win 2000 machine with a 800mHz PIII and 256MB Ram with no issues. Of course she only browses the internet and prints a picture or two every now and then. I would go with XP over Vista unless you are going to get more Ram. Also keep in mind that these machines do not have floppy drives, modems or a CD-RW drive. That said if these are not issues then all of the deals here would be fine. I do agree with the 17" LCD especially for "older" eyes.
There are always deals popping up so waiting probably wouldn't hurt, although you could wait forever and be a slave to the hot deals and never get a computer. Deals come and go but you have to jump some time.
And no, you won't save much if any by omitting the OS on most systems.