Using Linear Regression to predict a future event / performance figure / speed figure

Okay, so, I am not asking this question for a school project or for a friend. I’ll come straight out and say it – Yes! I have a gambling problem.
My great love is for horses and horse racing. However, I tend to lose more-often than win. Thus, ideally, I am trying to reduce my losses – and for that, I need some help here.
I need to figure out how a horse is likely to perform today – given its past racing history.
Thus, the basic question I have for all you Excel experts is this – How do I use Linear Regression to predict the likeliest Speed Figure a given horse is likely to run today – given its past speed figure history?

So, the attached Excel Spreadsheet (Excel 2010 version) contains the relevant data that I would use to ask the question.
Column A contains today’s date.
Column B contains the race number
Column C contains the names of each horse in each race.
Column D contains the dates on which each horse has raced.
Column E contains the speed figure each horse earned on any given day that it raced.
Column F contains the question I am asking based on each horse’s racing history.

The real truth though, is that I am trying to understand Linear Regression – through a game I understand.

Thank you in advance for all good answers.