Yes it is. Sounds like the samsung doesn't play AAC files. This is another name for mp4 files, or mpeg4 (the successor to mp3), which also happens to be used by iTunes and iPod as default.
To convert them to mp3 in iTunes, goto edit->preferences in iTunes, click the advanced tab, then the importing tab. Change it to import as mp3, either 160 or 128 kbps (160 is better but will not be hugely noticeable).
Then press ok, and highlight the non-mp3 files that you want to convert. If you don't know which songs are mp3 and which aren't, you can right-click one of the column titles (such as 'name' or 'album title' etc.), and from the box that pops down tick 'type' too. This will show what type the songs are: mp3 or aac. so now you can highlight all the aac files, and then right-click one of them and choose 'convert selection to mp3'.
now you can delete your aac files if you like, and then just copy the new mp3 files across as before.