There are a number of ways to do this and a few key things that should be understood prior to making any changes.
The most important thing to understand is that the DS images are stored under the Altiris Agent in a folder eventually shared as "Deployment", and from there, under Task Handlers\Images. All of our imaging tasks look for this folder coded into the task, not as a variable. Thus, you can't easily move the images.
NOTE: DS 7.5 will store images under the Package share along with all other packages and will be subject to very similar limitations.
However, within this limitation you still have a few options:
Each of these will be discussed briefly below.
1 BEST PRACTICE: Move the Altiris Agent.
Since the images are stored under the Altiris Agent, this is the best and supported method for moving the images to a different drive. This will work in both versions, AND the concept is shared with other similar issues, like moving packages and patches. The Deployment "share" and Package "share" are both created under the agent, so using this method fixes all of the issues, AND will be the same as in version 7.5.
2 Use a program that re-directs the image data to another location.
Not supported, but very successful to many individuals, this method works in DS 7.1 only because all images are stored in the same location. DS 7.5 will not work with this as well unless the entire Package folder is also redirected.
One such program is a Microsoft supplied program called LinkD and it may work for you as well. Instructions for using one version of this app are below:
3. Use HTTP Imaging.
This is the next best method per Symantec recommendations, for it is built-in to the product and supported. Imaging can be a bit slow using this method, but the process allows for direct store of images in any folder, without using GUIDS and such to identify them. IIS is used to create an Alias to point to a folder you create, and then when you capture the image, you point to that alias, and voila, the image is there.
For setting up the Alias in IIS, refer to: http://www.symantec.com/docs/TECH161430
4. Manually script the process.
This method bypasses the Symantec default jobs and uses some level of scripting you (the customer) makes. For instance, you may map a drive using VBS, then run Ghost manually with the same script, or something of that nauture. You (the customer) would be responsible to ensure the script works, rights are in place, etc., but you'd also be able to control completely the destination of the images.