I need the discussions that happened between 20May2002 and 30May2002
in the UsenNet news group alt.tv.buffy-v-slayer

I think you are in luck.  Google Groups offers a handy way to quickly
search through old usenet messages.  Using the Advanced Search area of
Google Groups, I was able to specify your requested dates.  (Since
this is a long URL, you may need to copy and paste it into your web
browser.)

http://groups.google.com/groups?safe=images&ie=UTF-8&oe=UTF-8&as_ugroup=alt.tv.buffy-v-slayer&lr=&as_drrb=b&as_mind=20&as_minm=5&as_miny=2002&as_maxd=30&as_maxm=5&as_maxy=2002&hl=en

If you prefer, you can use the "Advanced Search" option to narrow your
search further if there is a particular topic you are trying to follow
on those days.
http://groups.google.com/advanced_group_search

I hope that helps.