Good eveing. We need to go back to the beginning a bit here.
If you haven't got the tank yet, the bigger the better in my opinion. The size you have said is fine but if funds allow go a step bigger.

It is very important to set the tank up correctly before you even think about putting things in it. You clearly want perculas (clowns) which is fine and a pair would be fine.

Have you researched everything you need for the tank?
ie what lighting, filtration etc you need to use, or would you like us to guide you through that?
Are you having a sump or not?
Are you looking to keep fish only or do you wnat to dabble with corals at a later date?

If you can give me an idea as to how much planning you have already done we can advise more specifically to help you through your setup.

It can be costly to set up, and takes many weeks to be ready for your first livestock (which also need to include cleaner shrimp& turbo snails...maybe a few hermit crabs).
It is well worth the wait

Unless you have a small tank you could leave the rock in for a bit before adding it to your main tank - to let it cycle / see if it cycles.

Ok first thanks adam for your email address, I dont have msn set up yet but I'll get right on it.

I dont have a huge butget so I think I'll stick to the 30gal tank I saw for £300, included in this price was a heater(not sure what wattage), hang on filter, salt and I think some bace sand. O also it has two stripe lights in the top that I'll need to swap over to aquraim one's.

Still researching, glad to find this site.

First i want to get a laod of live rock and grow corals, mushrooms anemone's, then later I'll get fish. Also I dont mind waiting a while for fish.

I've onlg been to my LFS twice but they have givin me alot of advise, but thats all really. Also I've seen a couple marine tanks.

Can someone please explain what a cycle is. I think this is refering to coral or live rock.

Sorry I meant 40gal tank

ok here goes....simplified!

when you set up your tank and add live rock to it it causes the tank to "cycle" and a lot of ammonia is produced which is harmful to livestock. As the days and weeks go by the ammonia is converted to nitrite which is still harmful, and finally it converts to nitrate which is a lot less harmful. Your tank is only ready to have fish and inverts put in it, when the ammonia reads at zero, the nitrite reads at zero and the nitrae is less than 20ppm,
The "cycle" is kicked in to action by the natural bacteria in the rocks.
The rocks (if a large enough quanity is purchased) also act as filtration in the tank, removing waste converting it to the harmelss end product nitrate

Can i use half live rock and half some thing else like say normal rock or rock I could collect myself. ????

you can buy ocean rock to bulk it out and keep the cost down but it isn't live rock so does not help filtration. Try to have more live rock than ocean rock though if you can.

Its prob best to fork out for the live rock then.

Once I set up my tank, put salt, skimmer, filter and heater do I need to wait a while (how long?) before I put my live rock in?

Also what is live sand and do I need this for my tank?

stuart