depends what uni you're applying to. if its sunderland, teeside or northumbria (or any 'new' uni) just write your name down and you'll get in guaranteed, in fact i bet its the same with most uni's.
there's literally thousands of websites that offer personal statement templates and advice, even sample ones you can copy.
i've been to 2 uni's so i had to write 2 personal statements. in both I simply expained the reasons why I wanted to study the course in question (also did computing my second time at uni), and tried to give the impression that I wouldnt quit in 2 months like most people.
most people cover the 3 main points:
1. Why do you want to study this subject?
2. What have you done in the past that makes you particularly suitable to study the subject?
3. What else have you done that would contribute to the course and the university community and makes you an interesting and unique individual?
most uni's want to accept you more than you want to get on the course. they get paid for it. give them half an excuse and they'll take you in. you've got nothing to worry about unless you're applying for a seriously oversubscribed course at a popular uni. if thats the case you need to compete for your place, and the best way to do that is with grades and impressing at interview, personal statements can be the deciding factor on getting an interview, so its worth putting a bit of effort in if you expect places to be limited on the course you want to do.
read these for tips and plenty of examples you can use
http://www.universityoptions.co.uk/parents/4/3.asp
http://owl.english.purdue.edu/handouts/pw/p_perstate.html
http://www.getintouni.com/
http://www.kent.ac.uk/careers/cv/PersonalStatement.htm
http://www.brookes.ac.uk/bigfoot/personal_statements