As a Linux user myself who converted to Mac, I have been through this very problem. My research shows that Mac OS X and Linux pretty much don't share any common file system formats except for good ol' (?) Microsoft FAT/FAT32. This makes the transfer problem ...well... problematic. Whats more, if you do copy your files out to FAT32 harddrive as your transfer mechanism, you lose all the owner and permission information, which can be catastrophic for some programs like Thunderbird, which you can run under both Linux and Mac OS X.
There are a number of options to transfer your files, depending on what you have a available to you.
1/ External Hard Drive Formatted for HFS+: If you have an external hard drive, consider the following. Many Linux OS' support Apple HFS+ file system format. This is usually via the kernel module hfsplus. I know that SuSE supports this and I suspect that Ubuntu does too. Check your distro and see if it supports this module. If it does, you can "sudo modprobe hfsplus", and then use the Mac (when you get it) to reformat your hard drive to HFS+ and then mount it on your Linux system. You can then do the transfer using the hard drive, keeping all owner and permission information intact.
2/ Live CD with HFS+ support: This is a variation on the above. If you go and get one of the live CDs that support HFS+ (SuSE, Ubuntu and others should do this - just find a distro that does it and get the live CD) you can run through approach (1) above even if your loaded distro doesn't support HFS+.
3/ iPod as a Hard Drive: A variation on this is to use an iPod as your external hard drive. If you have a big enough iPod, you can enable the disk mode on it, and do the above using the iPod. This requires that you get your Mac, and reformat your iPod to Mac format instead of Windows format, but that part at least is easy between iTunes and the Mac Disk Utility.
4/ SAMBA - you are there already, so I don't have to go through that.
5/ FTP - silly as it sounds, you could tar up all your files (thus preserving owner and permission) and then ftp them across to your Mac. To do this, all you need to do is get an FTP server running on your Linux box (pureftpd is a good one if you are looking, and easy to set up). Then just go to good ol' Terminal on your new Mac (this is a bash command line) and use the FTP command. Mac OS X is based on a version of FreeBSD (or OpenBSD - I can never remember which) and so all the Linux command line commands you know and love are all available from Terminal).
What did I do? I used the first of these options. I had SuSE 9.3 available and it supports HFS+. So I got my Mac, reformatted an external drive, mounted it under SuSE, copied my files to the drive, and then plugged the drive into my Mac. It mounted successfully to my desktop and a simple set of file copies later, I was done.
Good luck!
