I haven't had any issues with crashing or lag either napa182.
I haven't tested this on mirc 7 yet but I have tested it on 6.35 with xp, vista and windows 7. I will do some testing later with 7.1 on windows 7 and if I have any issues I will be sure to correct them asap.
Is your vista 64 or 32 [nas]peter?