Minimum version for export-import to work?

I have a blog using version 2.1 that’s hosted on a virtual server. I want to move it to www.ads-software.com and have already set up its home there. I exported it successfully from 2.1 but it won’t import to the current version 3.x, seems it’s too old. Since I’m abandoning the virtual server once this is done, I don’t necessarily need to bring this old blog up to the most current version of WordPress. The other blog I had was on 2.7 and it exported/imported just fine to 3.x. What is the minimum version I must upgrade to in order for the import to work? Do I need to take it all the way to 2.7? I understand I need to upgrade it incrementally, just want to know how many increments I’m going to need to do. Thank you in advance.