HDparm and disk tuning. 

http://www.linuxforum.com/plug/articles/needforspeed.html

One of the biggest challenges for digital video editing is to keep data
flowing to or from a harddisk at a good enough rate to keep pace with
capture / playback while leaving enough operating system free cycles to
actually perform the capture / playback generating the disk activity.

Linux ships with fairly conservative drive performance configurations to
support the lowest common denominator hardware and provide the most robust
settings for data integrity. Those wishing to push the envelope and
squease more perfomance out of their drives can use the utility 'hdparm'
to tune their systems.

 Test these on the command line first, then
put them somewhere in your boot-up process.

-W: write caching *see note*
-c: 32 bit I/O
-d: Use DMA
-m: Multisector I/O
-u: unmask interupt
-A: drive read-lookahead
-a: filesystem readahead
Tuning your disk using hdparm

/sbin/hdparm -c 1 -d 1 -u 1 -W 1 -m 16 -a24 -A1

On a PIII/500 with a 12Gig IDE harddisk my capture performance was..

Before Changes: 120x160 15 frames/sec

After Changes: 320x480 29 frames/sec

(quicktime/JPEG 80% video, 44100Mhz 16bit audio)

I have tried forcing sync's constantly using something like:

while true; do sleep 1; sync; done

And I have found after the changes above (and probably the best one, write
caching) that this no longer has any noticable effect.

I also turned off my swap space. You should have enough physical memory to
keep all your active programs in ram rather than in disk swap. If your
system swaps to/from disk while you are capturing it's going to cost you
deeply in performance.

I've been using 'xosview' to monitor performance while working and making
tweaks, and am able to tell visually what my changes are doing to the
system.

NOTE: You should read the hdparm manpage to get a full understanding of
what each of these options might do to your system. One perticular note is
that the '-W' flag turns on write caching, which vastly increases write
performance but at the price of risking data loss on a crash or power
failure. 

What resolution is a TV anyway? 

That depends.. See:
http://members.aol.com/ajaynejr/vidres.htm