Originally Posted by HolyAngel
Need a new ballast for driving the t5's, and new end-caps to plug in the bulbs.
+1 on that, do a "google shopping" search for "T5HO ballast kit" you'll come up with all sorts of results. Here's one from amazon. IMHO it looks good, but was reviewed by a moron.
It will be quite a job so I hope you're a skilled DIY'er. None of the bulb mounting holes will line up right because T5's are usually a little shorter than T8's. Also, the ballast may or may not fit inside the enclosure.
If you do it, be sure to post pics!