Credit Card Spreadsheet

I have started working on my debt-tracking spreadsheet, and have decided to 'brand' it as TheCreditCruncher.com which is the name carried by one of my blogs. I intend to get it to a state where I think it can be shared with the general public and then include it as a free downloadable file. I have sketched out the way I think I want it to work, although I am having to compromise a little...
I use a similar spreadsheet, but use one large sheet which just grows and grows (in fact I use one for every card or account that I have, and then link them together via a menu). This new spreadsheet will probably consist of one page per month, that way users will be able to check each sheet against their monthly statement. This gives me a problem in that if I automatically carry over an 'opening balance', that balance will automatically carry over onto future months sheets - The alternative would be to have to enter the opening balance manually - this would give us a neater graph where future debt is zero, however one could argue that any outstanding amount IS actually future debt, and every payment against the account should show that debt dropping. I need to ponder this and maybe get some opinions of other people before I progress to a final version. I also want to try the sheet for a few months myself so that I can be sure it does the job in a realistic situation.
I am also considering whether to add on functionality to track several cards or accounts in one master sheet - perhaps offer a single account version, two-account, three account etc... I am also thinking about whether I need a version which uses dollars as currency, and another for £GBP, or maybe I just remove the currency altogether?? One other thing I am thinking of is having everything available both as MS EXCEL and OpenOffice files so that anyone will be able to access the spreadsheets without having to be a subscriber to Microsoft products.
I have already settled on a colour scheme and a logo, but frankly I usually go 'off the deep end' on appearance and will probably have to come up with something more conservative before unleashing it on an unsuspecting public...