As da unc says, seahorses should not be kept with other fish except maybe a mandarin. Both are for experienced marine keepers only.

I have had a lot of trouble finding sites that I understand. There is either too much detail (scientific gobbledegook) or too many contradictions.

Here's what I've learnt after starting up a 700 litre tank in October.

Read, read, read and read more (dont' expect to understand it all though).

Find a good marine petshop.

Plan a quarantine tank as the stock you buy is way too expensive and precious to risk losses.

Don't expect it to all go right and your tank will probably look quite ugly at first with hair algae, diatoms etc.

Research (I wll give you some links later) and then ask questions here - rec.aquaria.marine.reefs as you get the best answers here. It is a newsgroup so if you dont' know how to access a newsgroup there is a mirror forum somewhere which I can find a link to for you.

Go slooooooow! Don't rush anything.

Have a huge bank account - several thousand would be a good start.

Budget for salt for water changes.

Buy heaps of test kits. (Phosphates, Calcium, KH, Ammonia, Nitrites, Nitrates, pH and more)

No, it is not just as easy as freshwater even once you have it set up but it is far more fascinating.

Many recommend cheap damsels as starter fish. Don't do it. They are aggressive and you shouldn't be adding any fish if your tank hasn't cycled anyway. I went with tank bred ocellaris clowns and they are fine.

Of course some people feel they are worth it just to see the MALES get pregnant. ;)

Many, if not most sea horse species have been way over collected and are endangered. They are also at risk as coastal wetlands are cleared for housing and resorts. The good news here is that a whole new business - commercial breeding of seahorses - seems to be rising.

One of the magazines has a regular column on them, "Horse Forum" in FAMA (Freshwater and Marine Aquarium Magazine. Next time you are in a big box store for book, check their magazine rack. You should find it there and be able to peruse that month's column.

There is also a seahorse e-mailing list:
http://www.poost.nl/seahorse/finmail.html

I subscribe to About Saltwater Aquariums mailing list. A couple supply that site with a lot of good info. Quite a bit is useful for any aquarist. But they obviously especially have a lot for newer marine aquarists. Go to http://saltaquarium.about.com/

And by the way, if you think that we have a lot of stuff in Immediate Help, take a look at their lists in the margins! ;)

Starting up in saltwater is a little more tricky, but once your tank is up and going, maintenance is be quite a bit like freshwater aquaristics. However, marine aquariums are often a lot bigger than freshwater systems. Many of the accessories, from the salt to the testing devices, are more expensive. Indeed one segment of the marine hobby is there because a $10,000 set-up is just the accessory every wealthy person's home should have. ;)

Obviously a lot of marine aquarists just like the fish or the reefs and aren't keeping the tanks just as a status symbol. There are also a number of subdivisions in terms of what kind of saltwater tank one might want. Those who come to the hobby from that Nemo movie (more honestly it would have been called Grinding Nemo) will probably come and go.

MACNA is representative of a group of the really serious marine aquarists, who include some pretty dedicated individiuals and some high rollers. http://www.macnaxvii.com/

Many large urban areas no have a marine club. Google your area and Marine Aquarium Society.

A number of those people speaking at MACNA have profoundly influenced the freshwater side of the hobby as they researched and wrote on things like the Nitrogen Cycle, water chemistry, diet, new technology and the like. So we are in their debt.