Trouble connecting my xbox 360 via ICS?

first off. I'm trying to coneect my 360 in hotel wireless scenarios via an ethernet ics through my laptop (windows XP Proff.). i've been doing it for the last couple years but they gave me a new pc and it won't work anymore.i keep getting insufficient MTU error when trying this. I tried using the dr tcp or tpc (ithink that's what it is) to change the MTU settings on my laptop but it doesn't work. there's no problem with the ics - the internet test is varified in a heartbeat - just that damned MTU! HELP!