well well. vista is one frustrating thing, indeed. i like the colors and some little gadgets and stuff, but overall it is a piece of doggie bag content.
to your printer, you need to give permissions, beside enabling printer sharing and private network setting. check out your firewall setting also. it sounds like it is a permission problem, inducing from the simple fact it prints after you log in again. weird indeed.
okay, this is what you do. i do not know if it is the way for the printer, but it should be similar:
printer options. sharing, advanced sharing, add, permissions, and give permissions to everyone on the darn list. vista will probably send you to hell that you do not have sufficient rights to do that and in that case you need to dig even further and go to vista registry and temporarily disable some fundamental functions. these may cause the entire system to crash and you will be in bigger trouble then. but dont worry, it just might not happen

. as to what to disable, i do not remember, it is one two or three registries. oh and at the time you disable the registries, your computer will be very vulnerable to internet pirates.
a lot of fun right?
good luck