I was having some DNS troubles running an XP Guest (Using NAT), and thought I would share my fix with everyone (I didn't see anyone post this "solution" anywhere that I looked).
The first problem was to overcome the default DNS assignment and manually put in the DNS in the guest (it didn't pick up from /etc/resolve.conf). This let me nslookup websites, but web-browsing was still not working. After a half-a-day searching, this seemed to fix most peoples (similar) DNS problems, but not everyone's (and certainly not mine).
It turns out the persisting problem was with the XP update that also gave ZoneAlarm troubles a while back: KB951748
After uninstalling that update, the DNS problems were fixed in the virtual machine.
Maybe this was common sense to others, but I just thought I'd post it up for other people like me