If you're rooted you can use drocap
If you're unrooted, then nope, besides ADB, the only way to take screenshots is with a home replacement that supports it, such as the Home++ that you mentioned.
If rooted, you can use drocap2 or ShootMe. I think they require root because they get the screenshot from Home. This is why no one can do it without rooting unless they use a Home app that works that way.
This is the only one I currently have uploaded for HL 1.2:
It's a Smoked Glass one. Not that great but it will do for what you want. It also changes all the highlights and stuff to blue. If you ONLY want to modify the tab, then you can remove a lot of the other files and just leave the 3 tab images and the trashcans if you want to change them (i didn't).
the one in /Deluxe/HelixModPurple.zip is set up to work with all version of helix donor and market as well as helix2