ODDs are a thing of the past. I can’t even recall when I last installed an OS from DVD. Thanks to WUDT and LiLi you can install any OS from a pendrive. But what if you don’t have any at hand? Are you screwed? Nope.
You just gotta have a spare partition or some spare space on your disk. Just go to Control Panel and start Create and format hard disk partitions. Or for the more tech-savvy, run diskmgmt.msc. Here you can resize, shrink, delete, create, … volumes.
After you’re finished with creating an empty partition which is at least 4GB in size, extract your Windows 7/8 ISO there. You can use 7-Zip, which is free. Then install EasyBCD, which is also free for personal uses. Just enter a random name and e-mail address and it will start the download.
Now start EasyBCD and click on Add New Entry. Select WinPE and specify the path to your extracted boot.wim file.
Click Add Entry and bingo, now you can boot this entry. After you finished installing the new OS, you can use this same utility for removing the old, unused entries, or move your boot partition to somewhere else, etc.