Here's the code. I hope it works for you. Db1 is your db, Db2 contains the macro you want to run:
Const strPathToDb2 = "<pathname to Db2 directory>"
Dim strDB As String
' Initialize string to database path.
strDB = strPathToDb2 & "Db2.mdb"
' Create new instance of Microsoft Access.
Set app = CreateObject("Access.Application.8")
' Open database in Microsoft Access window.
' Run macro.
app.DoCmd.RunMacro "<macro name>"
If you want the macro in Db2 to manipulate something in Db2, this should work. If you want it to manipulate something in Db1, I'm not sure how to make that work.