I have a HP pc that the hard drive was recently replaced and I have redone it to where I have all my programs on it. Can I simply take that hard drive and stick it in a new build as my main boot drive? Do I have to do anything other than connect and boot?
Chipset/device drivers are likely to differ drastically from one system to another, but, it might be possible to install the drive in the new build, and simply boot from the WIndows CD (can't gaurantee an HP Restore CD will work, likely not), selecting a 'Repair Installation' -type reinstall.
You have 2 problems.
One is physical, it can be very tough to do what you are asking because as stated above, the Windows install is set to work in another machine. Sometimes Windows will boot and "fix" itself if the 2 machines are similar in hardware. Most of the time though it will not even boot, and then a repair install can be done and get everything working most of the time, but the install can still be bugging and flakey acting. A clean install is best for a new PC.
The second issue is that if the HP install is done with the OEM Windows disk, you will not be able to activate the installation on the second PC. If you have upgraded and you have a retail version of Windows, this won't be so much of a problem but you still may have to call Microsoft and get a new activation code.