Is there a Service Pack for Win 98?

Not from Microsoft but there is an Unofficial Windows 98 SE Service Pack offered as freeware by exuberant software. Version 2.0 was released 5/03/05

This is only for Windows 98SE ENGLISH. I highly recommend that you should backup your system before installing the pack. You must have at least 32 MB of RAM.

It contains only operating system updates. It does NOT contain Internet Explorer 6, DirectX 9, Media Player 9 and their updates.

Features in version 2.0:
100+ hotfixes (Detailed list will be prepared soon).
Solves 512 MB of RAM problem.
256-color tray icons.
Better Notepad: MetaPad 3.5 (Optional).
Optimized swap file usage (Optional).
Better WDM and USB support.
Adaptec ASPI 4.60.1021 drivers (Optional).
Windows Scripting Host 5.6.
DCOM98 1.3.
OLE Automation Libraries 2.40.4522.
Dial-Up Networking 1.4.
Microsoft Installer 2.0.
MDGx's HTML Help Update.
TweakUI (Optional).
Command Prompt Here (Optional).
New Animated Boot Logo (Optional).
Microsoft Layer for Unicode.
Visual Basic 5.0 SP2 runtime library.
Visual Basic 6.0 SP6 runtime library.
Visual C++ 6.0 SP6 runtime libraries.
Updates JET 3.5 files to JET 3.5 SP3.
Supports 98lite 4.7.
Windows 2000/ME desktop icons.
Windows 2000 color scheme (Optional).
Supports custom "Program Files" directory.
Shows attributes column in details view on the Windows Explorer.
Semi-slipstreaming support.
Some tweaks (Optional).

Known Problems: If you have Crystal Sound Card (CS423x), and have problem with the sound, you have to upgrade your drivers.

http://exuberant.ms11.net/98sesp.html

How to Back Up the Registry in Windows 98
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q256419