even a couple years ago when i reinstalled win98 on a machine the service pack updates were no longer available. someone told me you could download the service pack from downloads.com but i was never able to do that. to even get internet pages to display i had to use netscape
I did an install of the original Windows 98 to a VM last year and I was able to fully update it using Windows Update. The trick was that I needed to upgrade Internet Explorer first, so when to Microsoft's WWW site and downloaded Internet Explorer 6 serperately. I was then able to use Windows Update to install all the updates, including the one service pack released for it.
However, if the original poster's machine has 2GB of RAM on it he should just install Windows XP on it. Windows 98 SE doesn't work with more than 1G of RAM and has problems with more an 512M. That much RAM also suggests the PC is relatively modern and won't have full driver support for Win98SE.
I wouldn't suggest using Win98SE unless you're stuck with a machine with less than 512M of RAM or you want to have a second computer for playing older games that don't work right on modern machines.
Also, if the eMachines PC has OEM Windows XP sticker on it, as it probably does, then you don't even need to buy a new copy of Windows. It's already has a licenced copy bundled with it, so grab a Windows XP install CD and use the key on the sticker.