I have done some research on this and have not found exactly what I am
looking for as yet.  I am looking for a harddisk based portable DVR
with a screen (atleast 20GB). I am going to use this mainly for covert
surveillance purposes. It should have a wireless video receiver which
can be manually adjusted (No preset frequencies). Should atleast have
the ability to receive signals from 1.2Ghz and 2.4Ghz wireless
cameras. It should have good video recording capabilities, atleast at
30 fps to record from high resolution color CCTV cameras. Should be
able to record from external video sources like DVD players, video
cameras etc. It should also have motion detection/scheduled recording
with on screen time/date stamps. This is not wishful thinking. There
are gadgets out there which are quite similar to what I am talking
about. However, most of these are lacking something or the other. They
are either low on diskspace or have poor video quality. My first
priority is excellent video recording quality, then 1.2Ghz and 2.4 Ghz
adjustable frequencies receiver, and thirdly a motion
detection/scheduled recording.

The following product comes very close to what I am looking for.
However, it is only upgradable to a 1GB card, and has preset
frequencies:

http://cgi.ebay.com/Micro-DVR-Recorder-1-GB-Memory-All-In-One-Pro-Security_W0QQitemZ260009139581QQihZ016QQcategoryZ48634QQssPageNameZWD1VQQrdZ1QQcmdZViewItem

Here are some more similar products that miss the mark:

http://cgi.ebay.com/MINI-DVR-VIDEO-RECORDER-W-WIRELESS-RECEIVER-CAMERA_W0QQitemZ180023540378QQihZ008QQcategoryZ48634QQrdZ1QQcmdZViewItem

http://www.dynaspy.com/index.php?cPath=30&osCsid=2ea93d14e9ec4dbcac60b315b94c300f

http://search.ebay.com/search/search.dll?sofocus=bs&sbrftog=1&from=R10&catref=C6&satitle=micro+dvr&sacat=-1%26catref%3DC6&sargn=-1%26saslc%3D2&sadis=200&fpos=80017&ftrt=1&ftrv=1&saprclo=&saprchi=&fsop=1%26fsoo%3D1&coaction=compare&copagenum=1&coentrypage=search

Thank you.