Tested with Bochs 2.6.6 on Windows Vista SP2.

Copy the sample config to a production config:

COPY bochsrc-sample.txt bochsrc.txt

Create an 8 GB image file:

bximage -mode=create -hd=8G "D:\QEMU VMs\Windows 98 SE NL\Win98SENL.img" -q

Add to bochsrc.txt:

ata0-master: type=disk, path="D:\QEMU VMs\Windows 98 SE NL\Win98SENL.img", mode=flat
ata0-slave: type=cdrom, path="D:\ISO\Win98\WINDOWS 98.ISO", status=inserted

Set the BXSHARE variable to the Bochs install directory and start bochs:

SET BXSHARE=D:\Apps\Bochs-2.6.6
bochs