you never mentioned what video driver you are using, also if you have changed video options
Im not sure how to find it but whats listed in synaptic is x11-driver-video-radeonhd
also i just did the top command and here are the results
"top - 10:24:39 up 21 min, 1 user, load average: 0.25, 0.75, 0.75
Tasks: 121 total, 1 running, 120 sleeping, 0 stopped, 0 zombie
Cpu(s): 34.3%us, 1.0%sy, 0.7%ni, 60.7%id, 3.0%wa, 0.3%hi, 0.0%si, 0.0%st
Mem: 2050536k total, 1993912k used, 56624k free, 82760k buffers
Swap: 35680324k total, 96k used, 35680228k free, 1507120k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
4576 root 20 0 52624 28m 4568 S 32.9 1.4 0:52.30 X
5932 Daves 20 0 49024 20m 15m S 1.0 1.0 0:01.79 konsole
5383 Daves 20 0 50932 23m 17m S 0.7 1.2 0:02.50 kicker
3727 root 20 0 5420 1836 1632 S 0.3 0.1 0:00.38 hald-addon-inpu
4938 root 20 0 50484 24m 5892 S 0.3 1.2 0:06.48 python
5364 Daves 20 0 30416 3184 1756 S 0.3 0.2 0:00.05 dcopserver
5380 Daves 20 0 50028 23m 17m S 0.3 1.2 0:04.73 kdesktop
5390 Daves 20 0 31288 11m 9.9m S 0.3 0.6 0:01.07 kweatherservice
5436 Daves 20 0 42636 14m 11m S 0.3 0.7 0:01.26 knotify
5488 Daves 20 0 207m 112m 18m S 0.3 5.6 0:23.13 firefox-bin
5979 Daves 20 0 2444 1112 824 R 0.3 0.1 0:00.61 top
1 root 20 0 1792 560 496 S 0.0 0.0 0:00.49 init
2 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/0
4 root 15 -5 0 0 0 S 0.0 0.0 0:00.84 ksoftirqd/0
5 root 15 -5 0 0 0 S 0.0 0.0 0:00.06 events/0
6 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 khelper
50 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 kintegrityd/0
51 root 15 -5 0 0 0 S 0.0 0.0 0:00.07 kblockd/0
53 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 kacpid
54 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 kacpi_notify
126 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 kseriod
166 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pdflush
167 root 20 0 0 0 0 S 0.0 0.0 0:00.32 pdflush
168 root 15 -5 0 0 0 S 0.0 0.0 0:02.12 kswapd0
211 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 aio/0
390 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 kpsmoused
407 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 ksuspend_usbd
408 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 khubd
426 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 ata/0
427 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 ata_aux
436 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_0
437 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_1
440 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_2
441 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 usb-storage
452 root 15 -5 0 0 0 S 0.0 0.0 0:00.20 kjournald
576 root 16 -4 3020 1712 392 S 0.0 0.1 0:00.11 udevd
1340 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 kgameportd
1539 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 khpsbpkt
1566 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 kmmcd
1634 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 kondemand/0
1671 root 15 -5 0 0 0 S 0.0 0.0 0:00.00 kstriped
1750 root 20 0 4064 976 592 S 0.0 0.0 0:00.00 mount.ntfs-3g
3255 root 20 0 5332 996 552 S 0.0 0.0 0:00.00 wlandetect
3402 root 20 0 1844 636 524 S 0.0 0.0 0:00.27 syslogd
KAFFEINE and all xine based players won't work correctly either and so far i've run through the gambit
You might try deleting /home/~/.xine/config
>Steve
do you mean the whole folder or the file
the file config in the folder /home/~/.xine/ 
>Steve
OK just did that and whoa it made a huge diff in the xine players except for the kmplayer its a bit choppy while playing the .mkv files, and
while running top I've notice my CPU for Mplayer 68% and level of to 54% while kmplayer is at 1.3 % of course the format that is playing is .mkv while but i only click on kmplayer is that normal suppose it is hmm learn something new
but mplayer won't even come on for any file and vlc is still behaving the same way