Combo Box help (3 Levels)

I attended a course in November and helped me greatly and for that thank you but was wondering if you could help.

I have data that looks like the following:

ID Name LoS BU Grade Office C/nc
1 bob ADV a 1 1 C
2 harry IFS b 2 2 NC
3 Jim Tax c 3 3 C

This goes on for ~1500 lines.

What I was asked was to run a report using combo boxes.

They want to be able to select a LoS in combo box 1 (only 4 of them)
In combo box 2 they want to be able to choose a BU specific to that LoS (Ranges from like 10-150)
Then from there a third combo box to choose if they want C or NC or both.

Then when they click "ok" it will run a report bringing in the data from the data sheet.

I have managed to create a form that allows them to choose either a BU with all C/NC or choose if its C/NC with all BU.

Hope this makes some sense. If not feel free to email me on hammerfan43@msn.com where I can try to explain it a bit better.