Parametric part size entry

[trent.chambers]

MEP 2011. I have created a parametric part which seems to work pretty well, but I can not enter custom dimensions. The part is a representation of an electrical panel with a default size. During insertion I want be able to insert the part either with the default dimensions or enter dimensions as necessary (width, depth,height). I have these data types as "constant" ( the other options are calculation. list and table and I don't want any of these do I?) I have the custom size flag checked.
During insertion, the values appear but are grayed out and can not be changed. The same is true when I select mvpart modify. This has been driving me crazy for hours. Any suggestions?
Thanks

[RobertB]

You don't want constant because that's, well, constant. ;)

Try the list option because you are using the custom size flag.

[intocad]

You don't want constant because that's, well, constant. ;)

Try the list option because you are using the custom size flag.

I was wondering the same thing, the list thing appeard to do the trick.

I am trying to go a step further and am not having any luck. After I place the equipment and enter in the values, (for example, I have a 'D' value that I set at 24) it prompts me thru the it is a custom size etc. dialogs. I create the new custom piece of equipment and place it in the model. Now I was wanting to go back and edit those values in place via the Modify Equipment command (change 'D' from 24 to 36) and was hoping that the equipment would update accordingly. But this is not working for me at all.
Is this poissible? If so, what should I check to fix this?
Thanks for any suggestions etc.

JM