Without using an add-in boot-utils you can have:
DOS + one of the '98x family (or ME) + NTWS + NTSvr + W2K-Pro + W2K-Svr + XP-Pro + XP-Home); or any mix of those.
You say you 'had': windows nt4 workstation, nt4 server, windows 2000 pro, windows xp pro, then installed '98 and now none of those earlier OS will boot...
Hardly surprising... When '98 went in it overwrote the XP version of the mbr with the '98 version; this disabled the XP boot-loader which controlled the multi-boot environment... You will also be missing the required bootsect.dos via which '98 will boot from the XP boot-loader (once it's restored).
There are various ways to restore XP control (also to establish the bootsect.dos) and complete the multi-boot to include '98. But rather than go thru' them all here... suggest you visit:
http://www.dougknox.com
and go thru' the item in the section in the XP Tips (right hand column) - installing '98/ME after XP.
It's one of many ways to go about it...
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Useful to understand:
The core requirement for assorted M$ OS in a dual/multi-boot (without using an add-in boot-util) is that the active Primary must be accessible to all installed OS at boot-time... If DOS/NT are installed then it MUST be fat16 - unless using an add-in boot-util. If no DOS or NT present then it can be fat32; if no DOS, NT '9x(ME) it can even be ntfs. (There are exceptions to these basic rules/conditions.) Fat16 is the only common format across all M$ OS - which is why it's often the best format to use (and also if C: = 540Meg or less). The active Primary is where all M$ OS will install their appropriate boot/start-up files. (There are workarounds to accomodate 'some' of the M$ OS boot-file problems - and allow fat32 in C: .)
But on this occasion (because DOS and NTWS/Svr are present ...) it does require that C: (active Primary) = fat16. Otherwise it's the same as if C: = fat32 (which is how Doug Knox discusses it - as he is not including the NTWS/Svr in his equation).
Need more help - post back?