Shoutbox

I'll back up the 'HTML is easy' crowd, and say once you've got the hang of it, you really can let the creative juices flow.
The W3C Validation Service is one of the most useful sites for any budding Web developer. It'll analyse your page, find errors, and tell you where they are in detail.

Note: if you don't use a DOCTYPE, the validator will guess, which may affect the results. Moral of the story - always use a DOCTYPE