Is it possible to make the client mine bitcoins with the pool while simultaniously solo mining name coins (or conncting to a seperate namecoin pool)?
That's not possible. The pool supplies the block that needs to be hashed. In order to do merged mining, the header of the NMC block has to be included in that block for merged mining to be possible.
namecoin and bitcoin use the same blockchain?
Little more complicated than that.
Bitcoin & Namecoin have different blockchains.
How merged mining works is a hash for the namecoin block header is put INTO the coinbase transaction for the Bitcoin block. Thus when bitcoin block is hashed it can be checked against both bitcoin and namecoin difficulty.
Since the pool server creates the blockheader if it doesn't contain the namecoin block hash in the coinbase transaction then any resulting hash can only be used for Bitcoin.
Your choices:
1) pick a new pool. Bitminter is a 0% fee PPLNS merged mining pool.
2) use p2pool. W/ p2pool you created your own block headers and thus could merge mine anything you want.
3) solo mine. Obviously w/ solo mining you have complete control over what you mine.