Can you use a USB drive on both a PC and a Mac?

Yes you can use a USB drive on both a pc and a mac.Most new pen drives will support both.However some USBs might not work on a mac.My Sandisk Cruzer works on both my macbook and my pc desktop. Make sure if your sister's usb is not write-protected ( its a slide-lock available on some USBs. Also since she is able to read the files, it is likely that the usb is definitely working on her macbook

Hmmm, have never had that problem. I wonder if it is formatted with something other than fat32?

You should be able to, this is very odd.

she can't transfer files *to* the drive? have her open disk utility and format the drive. then see how it works...

@glial - on a mac, we don't use fat32. our file system is hfs plus

Hmm. I've never had this problem either - and I have 6 Macs - both Power PC and Intel-based. I'm thinking it's the USB drive and I would check the manufacturer's site for Mac-support. Has she tried the drive on a PC? Did the drive come with a set-up disc? I've found that when something doesn't "plug and play" on a Mac, the culprit is usually the developer/manufacturer not automatically supporting Apple's Operating System. There's usually some sort of download available to fix the problem. Good luck!

for what it's worth, as others have noted, i've used every usb drive under the sun on my mac, included flipping back and forth with a pc (or several) --- and never any problems.

@samkusnetz - I understand, but have you ever used or purchased a flash drive formatted in hfs . I have been a Mac user since 1990 ;-)

never! i always format them as soon as i buy them...

I don’t know because i have never owned a Mac i have always been successful with a PC for my uses.