Newbie question regarding BALLASTS and BULBS

I hope someone can be kind enough to enlighten me on this.

Here's the deal:
I have a nice heat sealed reflector accompanied by a 1000 watt HPS bulb that I got off a friend who is no longer using it.

I am attempting by all means to go as budget as I can while straying away from CFL (which I will use to partial veg and for clones/seedlings..).

Frankly, 1000 watts in this hps bulb is just way too much for the area and amount of plants I am trying to work with, and on top of that I do not want that great of an increase to my electricity bills.

I have heard that you can program ballasts to work with higher wattage bulbs to run at a lower setting, something to do with the voltage? So my question is, if that is truly the case, how would I go about using a ballast to run what I have right now at the equivalent of 400w or 600w while still using this 1000w bulb? I am shopping for a (hopefully used and cheap) ballast, but am researching what my options are at this point.

Sorry this is so long, but I am really hoping someone can clear this up for me.

Thanks a lot in advance

1000 watt hps only makes my bill go up 30 bucks a month max...

it's a small closet area with a small amount of plants, i just think 400w or 600w would be more cost efficient for me, and i am trying to work with what i have if there is an option to do so.

any ideas guys?