Like OmegaStarScream, i'm unsure about your intentions...
If you're trying to monitor an address for transactions funding it, follow OmegaStarScream's advice and use an api, or install bitcoind and use the json-rpc interface (both are quite easy to do using a php script).
If you're trying to verify if a transaction is valid, i guess
https://github.com/Bit-Wasp/bitcoin-php might be usefull for you.
Anyways, before we're able to give you advice tailored to your situation, we need more info...