Para windows 98 la última versión es la 6.2
Para la 7.x lee
Cita: Requisitos del sistema
* Sistemas operativos compatibles: Windows XP; Windows XP 64-bit; Windows XP Embedded; Windows XP Embedded Service Pack 1; Windows XP Embedded Service Pack 2 ; Windows XP for Itanium-based Systems Version 2003; Windows XP Home Edition ; Windows XP Home Edition N; Windows XP Media Center Edition; Windows XP Professional 64-Bit Edition (Itanium) ; Windows XP Professional 64-Bit Edition (Itanium) 2003; Windows XP Professional Edition ; Windows XP Professional N; Windows XP Professional x64 Edition ; Windows XP Service Pack 1; Windows XP Service Pack 2; Windows XP Starter Edition; Windows XP Tablet PC Edition
* Pentium PC with 233MHz processor or faster (500MHz recommended)
* Microsoft Windows XP operating system
* Minimum 64MB of RAM (128MB recommended)
* Up to 50MB of hard disk space needed to install — after install, up to 15MB may be needed
* 256-color VGA or higher resolution graphics card (SVGA recommended)
* Minimum 800x600 screen resolution
* Microsoft® Internet Explorer version 6.0 or later must be installed on your computer, though it does not need to be your default browser
MSN Messenger 7.5.0324 for Windows - Español
En esta otra página supuestamente está una versión 7.x para win98, si queres intentalo.
MSN Messenger 7.x, 6.x, 5.x actualizado