Short answer: No
Long answer: You need to consider that Windows 7 will be shipping on October 22, 2009. Although you get a Windows 7 coupon with the Vista or XP license that is included with most PC's purchased now, this may not be a good value. The reason the coupon is a poor value is that most experts recommend performing a clean install of a new operating system. If you've ever done a clean install you know this means re-installing all of your applications. This can be a very tedious process. Please note that it is technically possible to install Windows 7 over Windows Vista. According to Microsoft Windows 7 may not be installed over Windows XP.
Next, as always there are significant changes occurring with hardware right now. Recently Intel introduced new Core i7 and Core i5 microprocessors. They use a new socket to connect the processor to the mainboard. This is significant because it means that if you purchase a PC that uses the Core i7 that has been shipping for a while it will not work with the latest Core i7 or the new Core i5 micro processors. Always remember that if you need a new computer today, this doesn't matter. If you have a functional PC today and can wait a short time you may wish to consider a PC that has the new 1156 pin socket. (The older Core i7's have a 1366 pin socket) For a full review of the new Core i5 and Core i7 CPU's comparing them to an older Core i7 please visit.
You will not find a time when it is "right" to buy a new computer. Simply set an arbitrary date and go for it. That said, we recommend making your arbitrary computer purchase date after October 22, 2009 so you can get Windows 7 on your new PC and getting a PC that supports Intel's newest 1156 pin processor socket. It is possible to get PC's that support the new 1156 pin socket today. The 1156 pin socket based system should be acceptable for all users except high end gaming since current implementations only allow two way nVidia SLI or ATICrossfire at this time. Computers with the new 1156 pin Intel socket just may not be in stock at Best Buy or other stores. So you may want to consider another source that can ship you a new PC and let someone else who is less informed than you are help Best Buy clear out their aging inventory.