Writing regular expressions can sometimes be a real pain, especially if you are not used to them. Rather than trying for yourself to make a regular expression you might want to think about looking for regular expressions that other people have made. Rather than reinventing the wheel to prove you can do something,using free third party regular expressions can save you a lot of time.
The RegExLib or regular expression library is a great resource for finding any regular expression that you are looking for.
A good example of a regular expression that everybody seems to use at one point or another is to match an email address. Using the search function on the site I was able to find 98 different expressions that either matched email addresses, or had something to do with them.
What makes the site a really great resource is that every expression is given a description, a rating and an example list of what it matches and doesn't match. You can also run a quick test on the expression to see what it can do. This way you can see straight away if the expression available is going to do the job you want it to do.