Namecoin is the software and the blockchain.
Dot-BIT is the DNS servers, tools, wiki resources and support forum.

If you donate here, it'll go to the namecoin software author (vince) who promised a least 30% to "other developers and promoters"*.

So, they are pretty much the same, except people are differents :p
I don't want to steal the bitDNS bounty neither, so, donate to vince who initiated all this (i'll track him with my whip to get some BTC :p).