create a new module or use an exisitng module and use the following syntax in the declaration section...
Public varname as vartype
Now you can access this anywhere at anytime.. Just so you know, in order to get the value of this variable into a form somewhere, you probably will have to create a simple function to return the value of the variable.
function fGetVarName() as vartype
fGetVarName=varname
end function
Hope that helps...
Doug