As noted by phoenix, in the comments to the question, don't use the <marquee>
tag. If you're able to go with a jQuery solution there's quite a few news-tickers on offer, including this one: jq-liscroll/scrollanimate.html.
Edited, it might be worth taking a read of this thread for insights into some of the problems/solutions related to news tickers:
What's a good bit of js or jQuery for a horizontally-scrolling news ticker?
Edited, in response to the OP's question in the comments.
Using jQuery and Ajax doesn't seem to be particularly difficult or contra-indicated, if you look at the results page for 'jQuery + ajax' there's a significant number of results, suggesting that the two go together. Admittedly, the number of results may indicate difficulties, too. But I'm afraid I can't help much, since I've never tried to couple the two together. Or used Ajax at all so far...sorry.