Combo RowSource dependant on formula

[Slayboy]

I'm trying to make an electronic leave card system for my department at work and I am currently working on a leave entry form.
What I want to do is set a combo box for day type to use a limited value list of FULL;HALF to display whether it is a full or half day to be requested (and I only want a half day to be possible when someone enters a request as a single day, eg say they want 3 and a half days off then they have to enter the three day period and the half day as separate entries)
So to achieve this I thought I could make the value list dependant on the difference between the 'from' and 'to' dates, if the difference is 0 then the value list is HALF;FULL otherwise it is only FULL.
So basically I just need to make the value list come from a formula on the form, can someone tell me how to make this possible?

 

[Slayboy]

Can no one help!

Please can someone help me with this, I can't believe that there isn't a really simple way to do this, I just seem to have a mental block on it right now!

 

[Mile-O]

Can you redefine what you want and post an example of sample data/form as I'm having trouble working out what it is you want? Thanks.

 

[Slayboy]

An attempt to clarify

Basically, I want to safeguard against someone putting in a request for leave for say, from:29/04/04 to:30/04/04 which is 2 days, and then inputting 'half' into the day type, as it would be ambiguous (ie does it mean both days are half days, one is a half day and the other a full etc) The only way I could think of to stop that happening and make sure the leave requests are always properly defined was to have the options on the day type field dependant on the dates input.
At first I thought of maybe putting in some kind of validation rule so that 'HALF' could only be input into the 'day type' field if the leave 'to' and 'from' dates were the same, but I could make thant work.
Any ideas or suggestions? Is this a bit more clear?

 

[Slayboy]

Still not clear?

Am I still not being clear enough about what I need? Someone must know a way around it?

 

[Mile-O]

Are you making the user just type the start and end date for their holiday?

I'd have a subform where they typed each one in and selected the day type like in the example attached.