I am on a multiplayer server and am trying to create a lava fountain in front of my door. I have it enclosed in an area so the lava won't block any routes. The only problem is that I can't get the lava to flow. I've been told that I just need to put a bucket on top of a block and it should start flowing if I've got a step layout going down around the lava, but it doesn't work, the lava just disappears. Please let me know if I need multiple buckets or am missing something. Thank you.
I'll be adressing both water and lava in this answer.
First of all, Lava sources, unlike water does not spread on the overworld. (more info..)
Now, SMP still has several bugs, one of which is a problem with the bucket handling on the server. This is typically shown, as your bucket emptying and the water or lava you just placed suddenly dissapearing.
Luckily, the Modding community has already made a fix for the server for this problem as a class replacement for the server(as part of llamacraft)
This class replacement has to be done on the server by the server administrator.
This is currently not working in Minecraft Multiplayer (but works in single-player). See Minecraft SMP bugs for this and more bugs in Survival Multiplayer.
As a work-around, most players find a natural source of water/lava and craft around it to get it to flow wherever they want it to flow.
[Edit] I've noticed that water and lava work on some unmodded servers, but not others. On the ones that lava does work, it seems like it flows down but rarely outwards (water flows outwards though). Try placing your lava on a wall rather than the ground.