It sounds as if you have a Hydrangea Macrophylla. These come in two flavors, mophead and lacecap. You probably have a mophead.
These can grow to different sizes but assume 5x5 if you do not know the variety. If it can grow to 5x5 where it is currently planted, you do not need to prune it. If it gets out of bounds, prune it by the end of June as the stems begin to develop flower buds in July-August.
Your shrub is now suffering from transplant shock so I am not sure how this will affect flower bud production for Spring 2011. Just keep it well mulched (3-4") and watered. If winter is dry and the ground has not frozen, water it thru winter. Once the shrub goes dormant in the Fall, you can water once a week or once every two weeks if there is no rain.
During summer, the shrubs may wilt in the afternoons but they should recover on their own by next morning... usually much earlier than that. If the wilting episode is dramatic then immediately water with 1/2 gallon of water. Otherwise, insert a finger into the soil to a depth of 4" and water (1 gallon) if the soil feels dry or almost dry.
All hydrangeas wilt during the worst of the summer months, especially when the day happens to also be windy so water the night before a day when the weather service issues wind advisories. These wilting episodes will diminish as the plant becomes established in 1-2 years. The amounts of water suggested above apply to a new small hydrangea. Add 50% more water if your soil is sandy. Add more water too if your hydrangea is older/bigger. Try to water when the soil starts to feel dry because if you water too much, the roots could develop root rot (if they sit in water for long periods of time). The best way to water is to do it very early in the mornings and water the soil, not the leaves. Watering leaves can promote leaf spots and other fungal problems.
You did not specify how many hours of sun they are getting in this new location but I would try to provide it some shade during the harshest part of the summer months. Here in Texas, the leaves sunscorch by 12pm but as you go further north, they can get more sun. If you observe that the leaves turn all yellow -INCLUDING THE LEAF VEINS- then the leaves are getting too much sun. You then need to consider moving it elsewhere or you need to provide some sun protection.
There may be now a few leaves that begin to brown out from the edges inwards. This could be lack of water or because it now has fewer roots to provide moisture. No need to worry unless it is widespread.
Do not fertilize them now because they are suffering from transplant shock and are stressed. Instead add some weak fertilizers like liquid seaweed, liquid fish or coffee grounds but stop by the end of June. Starting the next growing season (2011), you can add 1 cup of compost, manure or cottonseed meal in June for the whole year. You can also apply the weak fertilizers between 2-weeks after your average date of last frost and by the end of June.