I think you will learn more if you clarify your question by stating why you want a HTPC, (for example: rather than a workstation or a stand alone blu-ray player). Here is a list of the range of possible purposes for a HTPC that I collected last year, (some of this is outdated):
What is an HTPC?
HTPC stands for Home Theater Personal Computer. It is understood to be a synonym with "Media Center PC", however the HTPC name implies use with a full home theater setup. Really, the best definition for an HTPC is any computer with special harware and/or software to make it more suited to audio and video playback and/or use with audio and video equipment than a normal computer. I think the best explaination for what an HTPC is is what it is used for.
What can an HTPC be used for?
-Playing/Ripping/Burning/Cataloging Blu-ray disks
-Watching, timeshifting, and recording analog TV (OTA and analog cable)
-Watching, timeshifting, and recording digital TV (ATSC, DVB-S, DVB-T)
-Watching, timeshifting, and recording unencrypted QAM (unencrypted digital cable)
-Listening to and recording FM radio
-Upscaling video to the native resolution of a display and processing in realtime
-Playing/Storing/Remotely Acessing/Transcoding MP3s, OGGs, WAVs, and many more audio formats
-Playing/Storing/Remotely Acessing/Transcoding WMVs, MPGs, MOVs, and many more video formats
-Home theater gaming
-Listening to internet radio
-Watcing internet television
-Managing multizone audio
-Recording/Viewing HD video via HDMI
-Recording/DACing audio via S/PDIF
-Controlling equipment that uses IR (TVs, projectors, receivers, etc.)
-Turning lights on/off, locking/unlocking doors, opening/closing curtians
-Home theater web browsing
-Internet video chat
-Acting as a Jukebox
-Emulating arcade games
-Saving money!!! (an HTPC combines all these features in one machine, often costing less money compared to separate or proprietary equipment)
Some of these require special hardware that is not found in a normal computer, but others just need certain software, some of which is free. If these features interest you, an HTPC may be right for you.