I�m not sure what software your card provides, but have a look in the options to see if you can choose what format the recording is in. If so, go for DivX AVI (you'll need to install the free DivX bundle if you don't already have it). It sounds as if the recordings are being made in some no/low compression format.
If you can't change the format, try using different software to record with: WinAVI Video capturer, STOIK Capturer, VideoLAN and VirtualDub all offer capture functions and are free - one of them should get reasonable results with your card! STOIK seems to be the best with my setup, but yours may be different - it also converts to DivX, so an "hour long" (40-45 minutes with ads removed) prog should be around 350MB.
If you want these to play on any DVD player, you will need to convert them to a suitable format. Nero does this "in program", though I find it quicker to use WinAVI Converter ($30 or free for an older version) to convert the file to MPEG first and then use Nero. SUPER (free) will also to the conversion, though I find it less reliable than WinAVI, Of course, if you have a DivX compatible player, or only want to watch the progs on a PC, then you can just burn the files to a disc as data.
VirtualDub, though not very pretty, also allows you to edit your captures (I'm assuming they are saved as DivX/AVIs as mentioned above) to remove ads etc. You'll need to check that both the video and the audio options are set to "direct stream copy" or you will end up with another massive file.
If you can't re-record your files, try SUPER or WinAVI to convert your existing files to AVI; his should reduce the file size.
If you really have to go down the screen capture route, I�ve used DebugMode Wink (free) for training �films� but the output is to a Flash file, which may not be good enough for your needs. Bobyte�s AVIscreen Classic saves to AVI (!), but I vaguely remember trying and