I'm going to make myself look like an idiot now but what's the difference between Passive & Active speakers? (My guess is you need a seprate amp with Passive but not Active?)

Thanks! :)

Hi Gazz,
You've got it spot on.

Passive- requires an amp.
Active - has a built-in amp.

Some things to bear in mind.

Actives will normally have an XLR connection (audio input). This type of connection/cable is very good at reducing background noise pickup.
To make best use of this, your mixer will need to provide XLR/Balanced outputs.
If it doesn't- you can get adapters, but you'll lose the noise immunity and you'll hear some hissing coming from the speaker.

I've gone Active, but keep my old Passives+Amp as backup.

One other possible benefit of actives is that they can be "bi-amped", so there are actually 2 amps in the cabinet.
One amp is tailored for Mid+Bass, the other for the tweeter. This should give a clearer sound compared to an equivalent priced passive system (with one amp doing all frequencies)