No, in 9.x Python has no ability to customize the user interface. There may be some aspects of UI customization for Python in 10.
For 9.x, you can either use VBA, which has an IDE built into the ArcGIS Desktop applications and can utilize ArcObjects along with built-in UI controls, or a 3rd party IDE and compiled programming language such as Visual Studio 2008 and C# or VB.NET. VBA is not supported (but may work) in 10, but not future versions, so if you want a long term solution a compiled DLL is probably your best bet.
See this page on the Resource Center for the options for developing for 9.3: http://resources.esri.com/arcgisDesktop/index.cfm?fa=forDevelopers