WSUS alternative [ low budget :( ]

WSUS alternative [ low budget ]

hey geeks

i am an admin of a small company. we have some
windows xp clients and some are still windows 2000.
my biggest headache is how i could make these
machine update within their account...it simple
doesnt work as it always asks for admin
permissions. now i know that WSUS is a solution to
my problem but we dont afford it.

is there an open source solution for my needs? or
something which is automated and works well? i want
to make sure that all clients are updated whenever
an update comes out.

hope i was clear in my replies and thanks so much
for your assistance !