If you place a Bid for 1,000btc @ $0.175 each and also have $0.00 balance in your mtgox.com account, then there will be an inactive bid for 1,000btc.
If you had or place an ask for xbtc @ $y and a trade occurs involving the asked amount, then you will have $ balance in your mtgox.com account which will then activate your previously inactive bid, or at least part of the bid will become active and the remaining amount that cannot be accounted for, due to lack of enough funds, will remain inactive.
Additionally, it appears this may also show signs of some sort of bug.
e.g. if lowest ask is xbtc @ $0.07 and an ask for 10btc @ $1.00 become active or is placed, will the bid match the lowest ask and result in a trade for 10btc @ $0.07 each for total cost of $0.70? Or will the trade result in 10btc @ $1.00 each for total cost of $10.00? Based on what happened, it appears that if you were to, right now, bid for 10btc @ $10.00 each, that you would buy 10btc for a total cost of $100.00. I am not willing to test this theory to confirm, however. ^_^