Unfortunately, it doesn't look like there's anyway to get ALL the information last.fm has on your track plays.
If you were to use last.fm's web services, you will only be able to get playcounts for your top 50 most-played tracks. And if you want the timestamp each track was played as well, that information is only available for the last 10 tracks played.
You could get more information (though still limited) if you got the data from your actual last.fm profile rather than through the web services. Playcounts are available for your top 500 most-played tracks, and timestamps for the track plays go back exactly 2 weeks.
If you wanted to be really hardcore (and didn't care about timestamps), you could parse through your weekly charts for every single week and accumulate the track playcounts. But again, the weekly charts are limited to your top 500 most-played tracks, so assuming you never play more than 500 tracks per week you could theoretically get a complete set of playcount info with this method.
EDIT: My bad, after taking a closer look at the web services, it appears that it if you use the weekly track chart data (weeklytrackchart.xml) then it is NOT limited to only 500 tracks/week, so you should be able to get a complete set of playcount data regardless of how much you listen to each week
