There are pros and cons to each but I will just go over some things to think about.
Price: if my memory serves me the A75 is a fair bit cheaper than the S410 which is nice because it decreases the amount of worry about your camera getting lost/stolen -and it saves you money
Form factor: the A75 isn't as small as the S410 which can be good and bad. If you have large hands the S410 can often be too small to use comfortably whereas the A75 has more of a grip that you can hold onto while still remaining small enough that it isn't a problem to carry it around.
Features: the A75 offers full manual controls which is a huge plus; however, some people won't use the manual controls and would be just fine with the S410. Keep in mind that you can shoot fully auto with the A75 as well so you aren't buying into something that is going to have a huge learning curve if you don't want to. For someone like myself I would enjoy having the manual controls play with.
Package: unfortunately the A75 doesn't come with rechargeable batteries and a charger as opposed to the S410 that includes both. However, using a standard battery like a AA can be convenient because you can use the batteries from almost any piece of electronic equipment you have kicking around in a pinch (remotes, discmans, alarm clocks, etc.) I'd have to look at pricing but rechargeable batteries for the A75 should you choose it would be a worthwhile investment. I don't believe they are outrageously expensive.
Photo quality: it is difficult to tell at a glance if there are any huge image quality issues between the two; both produce exellent quality images, especially in comparison to the vast majority of the current competition. Technically I think the S410 has slightly better image quality; however, without manual controls it doesn't matter too much IMO.
Hope that helps narrow it down for you. Personally, unless it is vital that you have a tiny camera I'd suggest going with the A75 and saving yourself some cash. It would be a funner camera any way you look at it (if you are at all interested in photography).