Is this a [link|http://groups.google.com/groups?q=csrss.exe+slow&hl=en&lr=lang_en&ie=UTF-8&selm=OHPGL%24NXCHA.2240%40tkmsftngp10&rnum=1|laptop]?
I found a number slowdown issues related to csrss.exe on google groups; few with the '400 involved... This was one of the few with a 'resolution' (such as it is). If this isn't a laptop, do you have bios setting differences, perhaps power management?