I created a blog with blogger, then went though their tutorial on how to have them host it but use your own domain name. You can find that tutorial here:
http://help.blogger.com/bin/answer.p...373&topic=8911
Since your domain name is probably pointed towards 3dcart nameservers you will need to open a support ticket and ask them to create a cname record for your domain name (in my case
http://blog.prosoundsupplies.com) pointing to the entity hosting your blog or forum (in my case ghs.google.com)
Hope that helps!