Newbie wondering about ver. differences; 4.4.9 v. 5.x

[oldognewtricks]

I don't know if this is the correct type of question to ask here - I built a sandbox about 3 months ago with the latest XAMPP. I know that it came with PHP 5.x [5.2 I think]. I am not at home right now to check it. I just found out that the host server is running 4.4.9. I have no control over the host, or host selection. I am going to attempt to get a database online using basic [i hope] PHP scripts to query the otherwise static database. Are there major differences in the versions that I need to watch out for? I realize that I will now have to get 4.4.9 installed on my sandbox. I plan on using Dreamweaver CS5 to get my pages built. The main site is built and managed by another person using Expression Web 2. I am also unaware if the master.dwt built in Expression can be somehow brought into my PHP for site consistency. I am open to all comments and suggestions.