http://www.jockbio.com/Bios/Henry/Henry_bio.html
After the season, Barcelona again tried to grab Thierry from Arsenal, but he declined. The Gunners, in turn, signed him to an extension that will keep Thierry in Highbury until 2007.
well, that means there are two ways for Barça to get Henry, and it is quite hard:
1- Barça agrees on a transfer feed with Arsenal, so Barça can negotiate a contract with Henry. This one is lesslikely because i don't see Arsenal trying to get rid of him.
2- They do like Real Madrid did with Robinho. They paid Santos Robinho's contract-breaking fee (that was something around US$40 million), i don't know how much Henry's fee is, but it is sure a pretty high one. I know Ronaldo is more than 100 million dollars, Henry should be close to that. This way it shouldn't matter if Arsenal agrees or not, it's just between Henry and Barça.
either way, it will be a hefty price for Barça, so i don't know if they are really bringing him in this year.
When his contract has less than 6 months to expire, he can sign anywhere in the world and the team would just pay a fee decided by some Arbitrators. But if he waits till his contract is over, he can sign the contract 6 months prior to its end and join the new team at contract end.
i don't know if you understood anything, but i tried.