I recently purchased an Acer Aspire One laptop running Windows XP Home. It does not come with a serial port. I wanted to be able to program (flash) my Rio Car player with the laptop. I bought a USB to RS232 adapter and voila, it works fine.

Here's a link to the adapter I bought:

http://www.cablesunlimited.com/products/Prod_Individual3.aspx?groupcode=I3274