Netbook vs. laptop. Hmmm. If portability is a big thing, and if processing requirements are not too demanding, the netbook is fine, especially for e-mail and browsing. If, on the other hand, you require higher resolution to see drawings, photos, large spreadsheets, etc., or if you need processing horsepower, the laptop is the better choice. As others have pointed out, netbooks do not have optical drives, so plan on spending another $50-60 for a USB optical drive. Figure adding another DIMM to expand the memory (be sure to make an exact match of DIMM [type 2 or 3] and speed or you'll likely have memory-related issues), but don't bother going over 4 gig of RAM. You'll never get the bang for the buck on this.
The minimum operating system I would recommend is Windows 7 Home. The Starter edition is nothing but cripple-ware, and not worth your time. XP is still around, and generally functions well, but be aware that it's support life from Microsoft terminates at the end of December (the last time I heard). Microsoft is trying hard to kill off XP. It has a bunch of security issues that have largely been resolved in Windows 7.
If you maintain personally identifiable information (PII), like Quicken/QuickBooks banking records or social security numbers on the computer, either netbook or laptop, you'd be VERY wise to use whole-disk encryption such as TrueCrypt (free!!!), but the caveat here is that there is NO BACK DOOR, so you'd BETTER make a full, unencrypted backup before performing the encryption, and choose a passphrase that you will have no problem remembering. The absence of a back door means that if you forget the passphrase, you're deeply and fully screwed if you forget the passphrase. The good news is that if your computer ever gets ripped off (who would ever do such a thing?), nobody will ever be able to compromise your critical business information. The encryption does not slow down the machine in any way, once it's been started, and the actual encryption is transparent to the legitimate user with the proper passphrase. To anyone else, the hard drive is utterly useless.