On the same day I reinstalled my pc, now win 7, and the problem is the same - can't type nor see anything in the chat
If I remember right, in the old days using a modified chatbox used to solve the problem, or installing some kind of software from microsoft - not sure which. lmgtfy and I'll be back with the results
So msxmlenu.msi is required, or hearing from several accounts it fixes the problem, the main thing is, it supposed to be in your halo folder
My portable version somehow doesn't include this, so I can't upload it for you :c