Learning regular expression

I am learning Regular Expression right now. Here is the example to pull the information on monthly posting activities of Mathematica Discussion Group.

url = "http://groups.google.com/group/comp.soft-sys.math.mathematica/about";
reg = "(?<=month/)\\d+-\\d+\">\\d+";
data = Import[url, "Source"];
ex = StringCases[data, RegularExpression[reg]];
ds = ToExpression[StringSplit[ex, {";", "-", "\">"}]];

Then we can use DataListPlot to produce a nice graph.