Why am I breaking so many screws as I am trying to drill them into my wall?

I just need to put up some blinds from Ikea. I live in Boston and the moldings (mouldings?) in this apartment are old hardwood. The walls are plaster. I have a hard time hanging anything. I just spent forty-five minutes trying to get six screws into the window moldings. Three of the screws broke. One was... show more I just need to put up some blinds from Ikea.

I live in Boston and the moldings (mouldings?) in this apartment are old hardwood. The walls are plaster. I have a hard time hanging anything.

I just spent forty-five minutes trying to get six screws into the window moldings. Three of the screws broke. One was stripped. The others went in, but took forever.

I am using an inexpensive cordless drill from Black and Decker. I tried changing the bit (both a larger and a smaller one): no luck.

What is going on?? Is my drill too cheap? Is the wood too hard? I asked the man at the hardware store today, and he said that as long as it wasn't metal (it's definitiely wood), the screw "should go right in." I haven't used power tools since I used to build sets in high school, but I don't remember having this much trouble with such a basic project.

Help!!
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