Yes.  That's what I was trying to explain, using "sprites"!  That works like a charm.  I was doing it wrong, though.  I was setting background-position with a negative number for the rollover when you can simply change the background-alignment.  Not sure if negative position is actually wrong or not, because it does work, but I do believe the background-alignment is the proper method if it's a simple "replacement" image.  I think I've seen the position method work when there is more than one image being used, such as using the same "sprite" image for several classes that have different purposes, so it contains more than two image states.  Theoretically, you could use one large image that contains all the images you need on the page, and just adjust the background-position as needed, but there's a limit to the amount of bandwidth you can save with sprites and a point where too many images in the "sprite" image would have a negative impact on page load times and rendering.  The use of a "sprite" simply eliminates the delay that is present on rollover if two separate images are used and the browser has to download the hover image separately.  Using the sprite method, the hover state image is part of the regular state image, so there is no delay when you mouse-over the link.

I think what Frank meant is that DNN does not provide for login images or login icons directly.  But it certainly is possible with css styling alone since many, many of us already are successfully doing just that in dnn.

JOHN GIESY
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The major search engines are using sprites themselves, for example Google uses sprites on its search pages.  Just right click and save the logo image above the paging table at the bottom of any search page.  Yahoo and AOL also use sprites on their pages, and many, many other well-known's are using them, too.  Logic would imply that they wouldn't be using techniques that they themselves frown upon, but in the world of computer logic when has anything been that simple.  And it's not like Google has to worry about its own search engine rankings, they could get away with all the no-no's if they wanted to...  Anyway, it would be a surprise if sprites had a negative impact on seo rankings considering the fact that the major players are employing sprites to help speed up the page load times of their own sites.   A small, two image sprite for a login icon doesn't have to contain any negative numbers, so in this case that point is irrelavent.  If, like Google, you decide to use a larger number of images in the sprite, the negative number coordinates might become a problem, and on the A List Apart site they reported that some mobile devices choke and freeze on sprites.  So, yes, always do your research, but in this case of a simple two image logo icon it's not necessary.

JOHN GIESY
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I do agree that sprites are a common use, however from what I read in particular about the FiR system was there was some question as to whether negative offsets would trigger the SE's into thinking there was content being hidden. I do think that CSS is the best option, however I have seen rare instances where the design / required effect called for more than one element that may need to be styled, and that was where I was going with the edit-the-ascx files comment (ugly and hard to maintain, as noted as well).