Hi amiface,
I have been using Nero - Burning Rom 5.5.10.48 as it was bundled with my Fujitsu Siemens notebook.
Load Nero, then the new compilation window pops up (do not use the wizard). There are several CD types you can choose from (I have CD-ROM (ISO), Audio-CD, Mixed Mode CD, CD EXTRA, CD Copy, Video-CD, Super Video CD, CD-ROM (Boot), CD-ROM (Hybrid), CD-ROM (UDF) and CD-ROM (UDF/ISO)).
I chose "CD-ROM (Boot)" from the list. After selection, there are different tabs to the right of the list: Info, Boot, ISO, Label, Dates, Misc, Burn. The tab "Boot" is open by default.
Within the "Boot" tab there is a field "Source of boot image data" where you can select "Bootable logical drive" or "Image file". Choose the latter and select your img file.
Below that field, I can tick "Enable expert settings" and choose a "Kind of emulation", e.g. "Floppy Emulation 1.44MB".
The window should now look something like this:
(By the way, I use WindowsXP with the free "UXTheme Multi-Patcher" and the "qlassic" theme.)
Finally click the "New" button. There is now a window "ISO1" where you can add some files, but you do not need to. Just burn it and it should be bootable.
Hope this helps.