If they were on the same drive partition that was partitioned/formatted on install of LinuxMCE 10.04, they could have been over-written. Hopefully, you made a full backup of your media, and can copy them over from that backup.
That's why I prefer the net install,... because I always leave my /home partition untouched as a separate partition. And working off a KDE install allows for an advanced use of the Gparted tool inside the Ubiquity install program on the live disk. That way, files, downloads, settings, etc. are all archived there for me to access,... Only LinuxMCE starts adding in the duplicate entries that that the drive might have in sub-directories.
It doesn't seems to mess up LinuxMCE, doing that... Partitions are largely transparent to the way the system operates, as far as I've seen,... The only potential downside is a risk of running out of space on /home, if it's set too small, and the aforesaid duplicates. Those things you can "fix" with external HDs or NAS drives, and moving video files over to them, and deleting the dups.