I see where you're going with this question. Prior to 1997, you had to purchase a less expensive home within 2 years to avoid being taxed on your home sale.
Now it is as has been stated below. You don't have to roll all of your gains (or any, for that matter) into another house. You certainly can though. There shouldn't be any effects regarding your purchase (whether cheaper or more expensive). It's just that in order to be free from the tax, you can not have gained more than $250,000 if an individual or $500,000 if a couple in your primary residence of at least 2 of the last 5 years.
An expert in that area can help you further, so if there are more questions consult a tax professional. - Thu May 21 2009, 15:57