I just transferred my site to them at the end of last week and the domain isn't resolving.

I'm using these two:

Primary Nameserver: DNS.SITE5.COM (64.21.152.7)
Secondary Nameserver: DNS2.SITE5.COM (64.21.152.8)

I am able to resolve the Site5 site just fine, and it looks like it is using those nameservers... How long ago did the site get transferred? It could be an issue of propagation- not all ISPs update their zone files as often as others, so it could take up to 72 hours or so before the change is viewable worldwide.

Brian