You have a lot of questions! Why don't you read up on lighting on this link. It will give you a good overview:
http://www.redearslider.com/index_lighting_basking.html
Here's some answers to your specific questions:
1. It you get a mercury vapor bulb be sure the one you get is specifically designed for basking reptiles. Just any bulb from the home improvement store will not do. Don't get one stronger than a 100 watt flood - they are powerful and too much of a good thing is bad. The socket must be ceramic (because the bulb gets so hot) and the lamp should be rated at least for the wattage of the bulb. If you have a 100 watt bulb then the fixture must be rated for a 100 watt bulb or stronger. If your fixture meets those criteria then it's probably ok.
2. The tube bulb you saw would not be useful either for heat or for UVB. The long tube bulbs are fluorescent - which is almost the opposite of a mercury vapor bulb. The fluorescents are cool whereas the MVBs are very hot.
There are tube bulbs made for basking reptiles that are very good for UVB. They are fluorescent and are found in the reptile section of the store. The package must say specifically that the bulb provides UVB and what percentage it provides (like 5.0 or 10.0) or it's not what you need.
If you get a tube bulb for UVB, it won't be hot - it will be cool - so you'll have to have a second bulb to provide the heat your turtle needs over the basking area. The heat bulb can be a regular household incandescent bulb. A lot of people use a 75 watt bulb. Whether it will be feasible to use a hood with a fluorescent tube bulb and also an incandescent heat bulb depends on your aquarium. It's not often done this way.
If you want to use only one bulb, then the only way to do it is with a MVB bulb. Any other configuration is going to require two bulbs - one for heat and one for UVB.
