The main reason halogens are not good to grow with is because the light they put out is the wrong spectrum or color,halogens also have a very low lumen per watt ratio when compared to most other forms of acceptabler grow lighting like cfl's,floro tubes & hid's.
With that being said as long as you keep it far enough away you can use them for supplemental light but you need alot of wattage for them to do alot of good..
However i would reccomend you find another light source,you can buy cheap 4ft shop lights from home depot for less than $10 & then get a pair of T-12 4ft 40 watt floro tubes that are called "natural daylight" for $3 a pair,this will give you the proper spectrum lighting & not cost alot at the same time,these lights run so cool you can let them touch the plants & they will not burn a leaf, i use the t-12's for vegging my mother plants & they work great.
Another very inexpensive option is to use compact florescents (cfl) as supplemental lighting,these are also very cheap,you can get 25 watt bulbs that equal 100 watts of light for $10 for a case of six bulbs at home depot or lowes,place as many of these around the plants as you can afford,the light bulbs are the twisty pig tail looking lights.
If you have to use the halogen just be carefull of the plants as well as paying very close attention to any fire hazzards,they get roasting hot at the bulbs & transfer the bulb heat directly to the outer protective case.
