SCR579X:

http://www.mdgx.com/add.htm#MSE
http://www.mdgx.com/upd98me.php#112309

9-30-2010 Update

SCR579X:
Replaced newer MSE 5.7 CSCRIPT.EXE + WSCRIPT.EXE with older ones from MSE 5.6 to make it compatibile with HTA. Now CSCRIPT.EXE installs in %windir%\COMMAND + WSCRIPT.EXE installs in %windir% (same as MSE 5.6 files). Experimental!
• Unofficial Windows 98/98 SP1/98 SE/ME Scripting Engines (MSE) 5.7 include: VBScript (VBS) 5.6, JScript (JS) 5.7, Windows Script Components (WSC), Windows Script Host (WSH) 5.7 + Windows Script Runtime (WSR) 5.7:
http://msdn.microsoft.com/en-us/library/ms950396.aspx
Unofficial MSE 5.7 5.7.0.16535 + VBScript (VBS) 5.6 for Windows 98/98 SP1/98 SE/ME [679 KB].
Direct download:
http://www.mdgx.com/files/SCR579X.EXE
More info.
http://www.mdgx.com/files/scr57.php
Requires MS IE 5.5 SP2 or newer already installed!
http://www.mdgx.com/toy.htm#IEX

CAUTION:
In case of errors with Unofficial MSE 5.7 (re)install MSE 5.6 [679 KB].
http://www.mdgx.com/files/SCR569X.EXE

Previous version:
5-14-2010 

SCR579X:
Reverted back to older JSCRIPT.DLL 5.7.0.16535 (from WinXP Q955360 Fix) 
due to WMP9 compatibility issues. Replaced newer (buggy) JSCRIPT.DLL 5.7.6002.22145 (from Win2000 Q975542 Fix):
• Unofficial Windows 98/98 SP1/98 SE/ME Scripting Engines (MSE) 5.7 include: 
VBScript (VBS) 5.6, JScript (JS) 5.7, Windows Script Components (WSC), Windows Script Host (WSH) 5.7 
+ Windows Script Runtime (WSR) 5.7:

Previous version:
11-23-2009

Reverted back to older VBSCRIPT.DLL 5.6.0.8835 due to errors with newer VBSCRIPT.DLL 5.7.0.16535:
Reverted back to older 5.7.0.16535 files from WinXP Q955360 Fix because of errors with newer files: