why would a positioned element not appear in IE7? (it appears fine in IE8…)
thank you…
Because you’ve done something wrong. 
It might be that the parent element is not also positioned properly. We’d really need to see a link to be able to say what’s wrong here. But positioning certainly works in IE7.
Not appear? A bit vague – as Ralph said we’d really have to see the site in question.
Though if you’re talking APO (position:absolute) inside a RPO (Position:relative) does that parent RPO have a haslayout trigger? If haslayout isn’t tripped IE will typically misplace/mis-align/not show
Another possibility could be the disappearing content bug – which is typically caused by poor use of comments – YES, I said COMMENTS! Comments if placed between floats or between a RPO and APO siblings can trip rendering bugs in IE7 and lower, and some builds of firefox as well. (Mostly the 3.x branch, I’ve NOT observed it in 4.x+)
Though again, no code becomes “This is why we can’t help you.”