No worries, thats what we're here for. Your laptop, and indeed almost all laptops made these days uses a 2.5" SATA hard drive. There are two main types, the standard Rotational drives (which have a disk inside that spins and a little magnet reader that reads your data). These typically come in 5400, 7200, and occasionaly 10,000 RPM models. The faster the spin, the faster the data acccess, with 7200 RPM being the best price / energy utilization / speed combination. 5400 RPM drives are too slow, 10,000 RPM drives use alot of electricity and not all of them will fit a laptop drive bay.
The other kind of drive is a Solid State Drive, or SSD. These are generally more expensive, and not available in as large a capacity as the rotational drives, but they are generally much, much faster across the board.
Drive prices are fluctuating right now, but a 750 GB 7200 RPM drive, which would be somewhat smaller than your existing one but much faster currently runs $99 http://www.newegg.com/Product/Product.aspx?Item=N82E16822136923
A solid state drive of around 250GB, which would be much smaller but much faster runs around $330 http://www.newegg.com/Product/Product.aspx?Item=N82E16820148443
Depending on what you use your laptop for, you may very well be able to comfortably live with a smaller drive. If you have alot of video files (movies, etc) you might need the larger capacity, but most windows installations these days average around 80GB utilization with installed programs.
As for how you install the new drive, the actually physically installing it part is easy. you turn off the laptop, pull the battery, open the hard drive bay, remove a couple screws, slide the old drive out, put the new one in. The tricky part is getting your data from one drive to the other. You can always reinstall windows on the new drive, but if you haven't done that before I reccommend you get someone to help with that the first time. But that takes along time and means you have to reinstall all your drivers and programs. Not something you want to be trying if you aren't familiar with the process. The better way to do it is to use what is known as a Hard drive Imageing tool to clone your existing drive to the new one. That requires specialized software and tools though. Your local computer shops should have that available as a service, though some of them will charge you an arm and a leg to do it.