Dynamic Combos

I'm having a brain dead moment and I'm sure someone with more clarity has a quick and easy solution for me so here goes...

I have a table in a database as follows:

value1 - valuea - entrya
value1 - valuea - entryb
value1 - valuea - entryc
value2 - valueb - entrya
value2 - valueb - entryb
value3 - valuea - entryf
value3 - valuea - entrye
value3 - valuec - entryg

So...basically 3 fiesl tree'd...so...what I need to do is pull that table in on the page load (and I have to do it on page load because we have problems with our data pulling at the moment and it takes about 5 seconds just to initiate a query from the database). Anyway...need to have 3 combo boxes to select:

Value#...then by selected that it will allow you to select ValueLetter, and by selecting that will allow you to select Entries.

The point is I want to use that initial pull and refresh the list of what the 2nd and 3rd fields have in them based on the 1st and second.

If I were to do this in sql it be similar to:

Value# = select distinct number from list;
valueletter = select distinct letter from list where number = value#
entry = select distinct entry from list where number = value# and letter = valueletter

If that is all confusing and stuff, let me know. Any ideas on how to pull the data into a grid or just an xml data pull and then pull out the values of either with those type sql restrictions dynamically?

Btw, getting the data is not the problem, how to pull out only some of the data from the grid or xml data to use as an array for a combo box is the problem.