Win NT 4.0 now Win XP-E HELP!!!!!

They sent someone to "upgrade" the systems at my crappy corporate day job.
I need to know what to expect as to stability above all else.  Any other insights also VERY welcome.
As is well known I'm not a fan of MS but, NT's been a solid, stable OS there.
XP scares me 'cause I don't know it
Thanks in advance.