|"its from the recovery disc that came with the laptop why?"|
Because it may not work. The recovery info is stored on a hidden partition on the orginal HDD. Obviously if you switch the HDD, you'll lose the recovery partition.
You can get a 160GB HDD for about $40 or up to 1 TB for about $120, with plenty of sizes in between. There are several brands to choose from but I'd stick with Samsung, Seagate or Western Digital. Have a look at Newegg or SuperBiiz. Right now, SuperBiiz has 10% off (up to $10) on all HDDs. Use coupon code SHOUT. The code is good until the 17th.
I don't know how much memory you currently have, but here's a link to 4GB (2 x 2GB) DDR2-800 memory for $54. That's the max your laptop will accept: