If you are planning on buying a good quality sound card for your laptop, I would recommend buying an USB/Firewire sound card rather than a PCMCIA CardBus card. The sound cards are usually very expensive, and if you buy a good one it will probably last for a very long time; USB/Firewire interface ensures that you will be able to use the sound card if you were to move to a desktop. These cards are also even more expensive because they are much smaller, so getting a 5 channel PCMCIA sound card would be very expensive. Also, the PCMCIA CardBus bus is slowly becoming more obsolete as the newer, hot-pluggable ExpressCard bus is being phased in.
On to the sound card itself; what you buy really depends on what you want to use the sound card for. For gaming, nothing can beat Creative Labs sound cards; which is rather poor at music because the sampling rate is locked at 48KHz. (Normal CD audio has a sample rate of 44.1KHz.) It has horrendous drivers, but custom kX drivers are available.
For music listening, then cards by M-Audio, E-MU, and Terratec are all good choices. (I'm not that experienced with audiophile cards, so you should consult someone with more in-depth knowledge; namely Arainach.) Also, you must bear in mind that for dedicated music listening then stereo speakers is superior to surround-sound speakers.
After taking a look at some Firewire cards, there aren't any that fits within your budget that also has 5-channels. The
Edirol FA-66 seems like to be a card you're looking for, but it is way over your budget at £200. (Cheapest in the US is $350) With ASIO support, both the latency and CPU usage should be very low.
Jam it back in, in the dark.