One easy way would be to buy a 12-volt transformer and wire a bridge rectifier into the output to convert it to DC, but it seems like it would be even easier to just go get a 110VAC-to-12VDC wall wart and use that to power the lamp. I haven't tried this personally or done any math on it, but I think it's worth looking into.
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If you're asking what I think you're asking you need an inverter. You have a 110 light you want to use on a 12 volt system. Correct? An inverter will take your 12 volt dc and make it 110 volts a/c. You can get small inverts for $20 and up. Watch "woot.com" they have them often. But a small one will have very limited power and probably will not run a computer. The power won't be clean enough for that.
If MR16 is the halogen lamp, the answer is "no." I found this on the Internet: "Most MR16 lamps are operated using voltages lower than 120 volts, typically 12 volts. Some MR16 lamps, however, operate using 6 or 24 volts. A transformer is needed to reduce the line voltage from 120 or 277 volts." The transformer lowers the line voltage to 12 volts, but this is still AC. You can convert this to DC with diodes and capacitors. Search "dc converter" for information--there doesn't seem to be anything useful on Instructables.
What are you asking? L