available for what? some hotels (like disney's) do a hold so you can charge items to the room account (park purchases, meals, room/spa services) so the amount of the hold is still available to you but just for those purposes- but if it ate up all your credit limit you would'nt be able to still go out and do an atm withdrawl or charge at a non hotel affiliated buisness. you have to wait until the hotel releases the hold.
you have to be careful though when hotels do holds-if they are'nt timely in running their accounts or don't do it in the right order it can cause problems and overlimit fees with your debit card. we had this problem with a couple of different disney resorts-they did'nt release the hold on the same pass as the one they posted the charges to the debit card on so when we went to settle the bill they were telling us our debit card had been declined

so i end up on the desk phone talking to the bank who says the reason i'm over my limit is b/c disney has a hold for more than the amount of the charges, but they are posting the charges as well. bank spent quite a while with the desk staff trying to explain to them that they had to do the release of the hold and the charges on the same pass to free up that held money to cover the charges. finaly got it straightened out but then when we got the statement we got hit with an over-limit fee

i called the bank, they told me to call disney who ended up crediting the cost of the fee to our card.