PHP/MySQL matrix entry/edit form

I need a PHP page/script that will manage the relationships between two tables. We have one table that includes vendors (currently has 18 rows) and one that has capabilities (about 60 rows). We want what looks like a spreadsheet with the vendors listed across the top and the skills down the left. Wherever a vendor has a specific capability, a checkbox should be checked. When the user saves the data, a third table should be updated with the values as tuples. For example, if the vendor "Process Lab" has a VID of 7 and the skill called "Weight Reduction" has an SID of 402, the script should insert/update a record that will include 7 in the VID field and 402 in the SID field. Each record in this third table might have a sequential ID. The skill IDs will range from 0 to 999. If the SID is divisible by 100 it will be treated as a category rather than a skill and it will not be used in the third table. On screen, the SID 400 would display "Analytical Services", and the details (including 402, Weight Reduction) will then be listed below it. This table has to be functional, not beautiful, it will not be used by the public. The table rows that are categories need to have a class assigned so they can look different than the other rows, but just enough that it's easy to keep track of where in the table you are editing. Alternate columns should be slightly tinted for the same reason, if you assign the class I can take care of the details. On the final site, the contents of the third table will be used to display those vendors that offer a specific service or to display which services are offered by a specific vendor. This script is just a visual way of letting the managers easily control what vendors are offering which services. I'm sure this is a simple task for those who have done it before but I'm having trouble getting started. This contract will be awarded promptly once a capable freelancer has entered an attractive bid.