Emachines tend to use cheaper componets to get the job done (hence the low price). I would find out what they are using under the hood and then make a decision. My friend had an older emachines (back when a Celeron 366 was not that low end) that worked great. Cost him $50.00 after buying the monitor and printer that had an instant rebate of $150.00. All together he only spent $300. He used that PC for some time -- with some major upgrades of course. Newer hard drive, burner, 3d card, ram upgrade.
As for the machines in general -- be willing to burn alot of time upgrading if you want to ADD, instead of replace. And in some cases you can only add (sound, video, lan are usually integrated). And to a very small degree (1 agp, 2 pci slots). And the chassis were terribly difficult to work on. Took me 1:30 to ADD another hard drive. The other mount requred me to disassemble the entire pc.
Either way, I am not bitter. HP is way worse garbage than emachines ever will be.