Most USB serial adapters you buy these days use a chipset made by a company called Prolific. We use USB-to-serial converters a lot where I work (we deal with a lot of devices that talk RS-232 or RS-422), and the Windows drivers for the Prolific-based units suck. They're cheap for a reason.
Go to Newegg or TigerDirect and search for USB-to-serial adapters that use the FTDI chipset. They cost a few bucks more, but unlike the Prolific-based units they actually work.
While not an option for the OP (since it is a laptop), an even better choice for desktop users is to check whether your motherboard has a COM header on it. Even if there isn't a DB-9 on the rear port cluster, the motherboard may still have on-board COM hardware; all you need to do is buy the corresponding rear panel DB-9 bracket & cable to allow you to use the motherboard's native COM port.
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