Problem resolved :-)

I just found out that when my colleague started Windows XP the Receive
Buffers started climbing.
He deactivated ICQ (v2003 build 3916) and Buffers went straight down to 0
again. Turned out that he had ICQ configured to using http proxy for
connection to and to resolve hostnames.

Do not know if this relates to my abend problem but for now i'm a happy guy