wedding reception spreadsheet: counting seats at tables (with sample)

Hello all...

We have spent a week of evenings beating on Excel and we just can't make a
calculation work... (maybe Excel 2003 can't do it?)
We are asking for help in making our wedding reception spreadsheet work...

Please see the attached Excel file... We are assigning tables and would like to have a
running total of seats per table...

For each party invited we enter Column A (the names), column B (the table #) and
Column C (the headcount per party).
We have Column H working... However we can't figure out how to make Column I work.
Column K shows what we would like to see.

Having the cell turn red if the headcount exceeds the table size is not vital
but would be an extra bonus.

Thanks in advance.

Sylvia & Mike (our wedding is on the 28th of this month).