The only program you need is the GECK. I'll move this to the GECK forum for you.
I'd suggest that first of all you hunt down the tutorial videos on YouTube, and bookmark the GECK wiki for reference. Get used to how the GECK is laid out, with its various drop-down menus for each item.
Each house is comprised of an exterior and an interior. The easiest way to find the exterior of the house you want is to either go to the Springvale worldspace, or to find Silver's house in the Interiors list and click on the doormarker to view the connecting door, then use your mouse to navigate your way around the exterior of her house to find the other intact house. If it has no existing interior, you'll need to add one (easiest way would be to right-click and Duplicate Silver's house. Look at the video tutorials for a few tips on this).
If it has an existing interior, you can skip this step. You'll find footlockers and cabinets in the Containers menu - they're self-descriptive so you'll easily find one for clothing.