for windows 95, you need to use a boot disk (windows 98 boot disk works) to fdisk and format the VM hard drive, and to "start with CD ROM support" to read the wind95/98 install disk.
download a cd iso version of a windows 98 bootdisk.
burn the 98 boot disk iso image on a cd
boot with the 98 boot disk CD and "with CD Rom support"
this should boot the VM into dos mode.
(note: look at what drive the CD rom is actually assigned, as the boot disk takes A:, and Diagnostics took D: my CD drive was E:)
run fdisk
create primary partition, etc.
restart, with the 98 boot disk cd again
run format
restart again
change the CD in the drive to the windows install Disk
change to the CD ROM Drive (E: for me) "cd e:"
check CD contents "dir /w" and llok for setup.exe
run setup.exe
laugh a gleefull laugh as windows installs
frown a sadsack frown as windows 95 client cant share files with its host
Note that even if you get this working, Windows 95 and 98 are not well supported in Virtualbox. They will run, but very slowly. Since your host if Windows XP, you're much better off using Microsoft Virtual PC as your hypervisor. – Charles Burge – 2017-01-03T07:08:55.177