Win XP - how do I stop something from auto-starting at startup

[Lobsang]

I know that's a messy title but I couldn't think of a sensible way of asking in one sentence.

In old versions of windows (9x) you'd go to system info, then startup apps (from the tools menu or something) and then uncheck something from the list.

In windows XP that's not there (sysinfo is, and the tools menu is, but no list of startup apps)

There's this stupid little program that installed it'self and tells me I have "75% free", but not what it is that I have 75% free of. Anyway I don't care what it is, I just want rid of it.