The HP 530 has a SATA hdd, so any of the hard drives at the Newegg site that link was provided for will work. A while back there was a limitation of 137GB hdds being recognized, this changed with the addition of SP4 in W2k, SP2 in XP, and Vista has it covered without any enhancement.
Because this is a laptop there is one consideration that hasn't been mentioned, and that is the speed of the hdd. Most laptops are shipped with hdds that operate at 5400 RPM, this is to conserve on the battery's A/H capacity, the faster 7200 RPM drives draw more wattage. If you are going to be working from home where the laptop can be plugged in regularly you may wish to go with the faster 7200 RPM hdd, there is a difference in performance.
As previously mentioned, you will need to make sure that you have the installation disc for the operating system, you should also have the twenty character product code when you go to install the OS. You may have to call MS to validate your computer, changing the hdd out will change how it is recognized by MS for updates.
If you need any information on removing the old hdd and installing the new one, check out this
Have you considered purchasing an external case for the smaller hdd so that you can use if for storage?
Edited by dc3, 27 June 2008 - 10:50 PM.