Anything is better than nothing, but pull-ups really are one of the cores of the P90x plan - if you're not doing them properly, or modifying in a way that really works you, you're not going to get the results you're after.
As you're in a basement, there are a couple of things I could recommend:
You could get a screw-in pull-up bar, like this one. It can go in a doorway or in a stairway, depending on the layout of your workout space.
Alternatively, one you can drill on to a wall would likely be the best option.
If you're not in to installing a honking great bar in your basement, you could get a metal hook or loop you could drill into the ceiling or high up on a wall. This way, you can run your bands through that to get a better angle.
As I said, doing an approximation and sticking with the programme for 90 days is great and you will become fitter, but pull-ups are one of the single best compound exercises on the planet, and with six or seven varieties in P90x you'll only get the intended results from doing proper pull-ups/bands.
Hope that helps!
I have this one. It's been good so far.