Is it possible to burn a large ISO file like 5.5gb into a single dvd ? if its not possible, can it be broken down to fit into 2? Any help is appreciated. Thanks.
Yes, you can use a double layer DVD. It is a different type of DVD and would need to be purchased separately.
The question of breaking it down into two parts is completely dependent on what kind of ISO file you have, and what you're trying to use it on.
Some more info on the file would help.
You can get DVD-DL (Dual Layer) discs, these allow you to burn up to about 8Gb per disc, although you need to make sure your drive is Dual Layer compatible as not all drives are. Plus DL discs a lot of the time work out more expensive than buying 2 single layers. So if you can split the ISO your better doing it that way.
If you have a Blu-ray writer you could also burn it to a BD-R, BD-R's can hold up to 25Gb per disc!
Some software like Nero does allow you to attempt to "overburn" discs, most discs can actually fit more data onto the disc than the manufacturer actually states and so if you overburn it you can put more on the disc, although most of the time it's not really recommended to go more than a couple of mb over (most 650mb CD's for example can actually hold 700mb but that is about their limit), 1.5Gb would be extremely dodgy, and if you do go too far over they do warn you that there is a risk that you could damage the drive as well as the disc.
There are also tools out there that allow you to mount ISO's on your system as a virtual drive
All of the above allow you to mount iso's as virtual drives on your system. Gizmo Drive is free, the other two do have trial versions but after that you have to pay, Alcohol 120% is superb as it allows you to rip data from various discs regardless of how badly damaged they may be.
Magic ISO - http://www.magiciso.com/ allows you to view an ISO file and extract it's contents to a hard drive, WinRAR (http://www.rarlabs.com) can also handle ISO files in a similar way.
If you create a virtual drive you'll be able to see the ISO file as if it were a CD drive and copy it's contents allowing you to split it in half.
Of course this all depends on what the DVD contains, if it's a game disc or software disc then you may find you have to burn it all on one disc for the software or game to work, you might get away with deleting certain non-essential items on there like additional demo's or DirectX, etc.
If the disc is just a general data disc with various programs on it (like for example a multiple emulators disc), or just stores files that can be used independently of each other then you can just split them into different folders, make a 3Gb one and a 2.5Gb one.
If it's a movie disc you can rip it using tools like DVD-Shrink http://www.dvdshrink.org/what_en.php this will allow you to shrink the quality of the DVD down from 5.5Gb to 4Gb (there is an option to shrink it to fit automatically on the disc) and remove non-essential parts to the movie, for example trailers, or extra footage. You can use DVD shrink with a virtual drive if you've used something like Gizmo drive, or you can use it with the extracted folder if you've extracted the disc using WinRAR or Magic ISO. Many movie DVD's do actually contain extra data on them that is unnecessary, this is done mainly to put people off copying them, many are deliberately made slightly larger than a standard 4Gb disc in the hope that instead of buying a DL disc or going through the hassle of re-encoding the files you will just purchase the movie.
If it is a movie you could also rip it to DivX or XVid format resulting in a file that is about 1Gb as opposed to 5gb, and then you could burn a couple of movies to a disc, of course whatever you intend to play them on must be DivX/XVid/MP4 compatible.
Also remember that you will need at least 11Gb hard drive space to play around with the ISO, 5.5Gb for the ISO itself and up to 5.5Gb for extracting (as well as a little extra space to ensure Windows has a bit of extra space to keep running - about 1Gb should do).