Need to allow members to buy "Credits" from points - How do I add Options?

I am a new user of vbbux and what I am trying to determins is how do I need to program my vbbux system to allow my users to purchase credits for a classified system.

Specifically, what I have so far is my user table with an extra field called "Ad Credits". I want to allow my members to be able to use some of their vbbux points to purchase credits. I was aiming for 100points = 1 credit for now but I am not sure where I should set this value.

So, can I used the advanced options in the bottom of the ADD OPTION area of the AdminCP to do this or do I need to program a php script to pull the value for the adcredits and then add the new adcredits and resave the result?

Thanks for any help and sorry for such a basic question!

-------------------------------------------------------------------
Here is an update
-------------------------------------------------------------------

OK, I managed to create a PHP file that does most of what I needed to do... my only issue seems to be that I don't know how to get my new php file to show in the history...

I managed to get the rest of it working including the order page, the confirmation before and confirmation when done plus the increase of adcredits and reduction of points....

So, can someone help me understand how and where the history is logged? Is it in a hook? I just can't seem to find it....

Thanks!

-------------------------------------------------------------------
Additional Help Needed
-------------------------------------------------------------------

I need to know how to use the "Input Field Settings" as well....

I believe that these should alow me to create options such as:

"Buy 1 Credit" using $adcredit with value 1

"Buy 5 Credits" using $adcredit with value 5

"Buy 10 Credits" using $adcredit with value 10

But I have not been able to figure this out and I don't see any documentaion on how this works.....

-------------------------------------------------------------------
STILL More Help Needed
-------------------------------------------------------------------

What do I need to do to allow my custom script or new option to update the number of items sold?

[CMX_CMGSCCC]

It sounds like u need to build a custom action.adcredits.php script file to do the calculations for u.

I'm extremely busy catching up with everything due to my 1 month business trip, otherwise I could help further. Maybe when I get caught up with everything I can help more.

-CMX