I had Vista installed on my Acer  5610z laptop and I was able to read my SDHC card, I now have XP and when i put in the SDHC card in the internal card raader nothing happens. I downloaded the drivers from Acer website for XP card reader and still nothing. I know the card reader is capable of reading the SDHC card, because it was working with Windows Vista. I tried everything and still nothing. Anyone have an idea or suggestion.
Maybe if you told us the MAKE and model of your card reader and whether it is internal or external, instead of putting all your question in the title and just a sad smiley where the information should be, you might get an answer.
Same computer CHANGED from Vista to XP?  Since you installed the XP drivers for you laptop's card reader, it should just work.He hasn't told us the SIZE of the SDHC card that is not read in XP, but this may be relevant

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a hotfix for Microsoft Windows XP that adds support for SECURE Digital High Capacity (SDHC) cards that have a capacity of more than 4 gigabytes (GB).