I may have misunderstood your question but that may due to the way you asked. I wasn't aware that you didn't have a floppy drive or couldn't have one. It is common for a PC owner with no bootable CD drive to hang onto a floppy drive which is dirt cheap and available as a bootable USB device too. It certainly save a lot of hair pulling.
Your situation is that you can only use Windows booted from a hard disk with no CD, floppy or USB support and want to install a Linux.
Grub4Dos and WinGrub are Grub on its own loadable into the PC in a Dos or Windows environment.
Once Grub is available, you can use it to boot any iso, suitably expanded, by replacing its isolinux boot loader with Grub. This just involves converting the isolinux.cfg into a menu.lst. The conversion is merely the syntax replacement of the command "LABEL" with "title", "KERNEL" with "kernel " and "initrd=" with "initrd ".
Thus technically
You need a Windows program to expand an iso file to a normal directory system.
Grub4Dos or Wingrub
Converting isolinux to Grub to boot the distro.
If you find a software that combines all the functionalities that is fine.
I can assure the above scheme works as it is a common trick to do away burning a CD and install the iso directly from a hard drive.
This thread show how 7 iso can be booted from a DVD or a USB device. A USB memory drive is just an external hard disk as far as Linux is concerned. This links has the examples of converting 7 isolinux.cfg to a menu.lst.
It is also an excellent example to show some distros installable/bootable from a CD/DVD can fail to work if the same files are moved to a disk.
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When it comes to questions and answers it is up to the original poster to explain his/her situation clearly so that members of the forum can formulate a solution. If the solution is inappropriate it isn't always their fault.
Nobody knows everything but there may be others who have done it before and are willing to offer their experience.
I have mentioned in Post #2 that Ubuntu iso may be unable to boot from a hard disk because its installer may keep going back to a CD device to fetch the files even though they are available in the hard disk. This may be the final brick wall.
I once wrote a script to boot every downloaded iso file from my hard disk, with a view to write a howto at the end. I found the iso files bootable this way are in the minority. I did not write down Ubuntu case but I am sure that I have tried it before. On my record none of the members from Debian family can do it. However newer versions may change that.
May be we have already answered your post. You just didn't believe Ubuntu installer has been written to fetch files from a CD drive regardless. I believe to alter Ubuntu's behaviour you have to hack its installer.
According to the above link you will find Slax, DSL and Mepis boot can be successfully installed if you try them. Then again you may regard this is not a solution because we don't know what you actually want.
Lastly if our effort has any value at all it is an independent confirmation that the current Ubuntu installer has been written to get the system files from the CD drive. You are therefore not alone.