My instruction would be a little bit shorter:
1) Download Debian installation DVD
2) To make things easier, do everything in QEMU folder. Admin rights are needed to do it. I use FAR manager for this purpose. It can remember your previous command lines, that is very useful feature for us.
3) Create disk via "qemu-img create -f qcow2 debian.qcow2 <size>G". qcow2 is used because it's size = size of data on it, not size of disk. Disk economy, you know. So, size of disk doesn't actually matter - you can even use 200G.
4) Use command line, I provided earlier. Specify debian.qcow2 as hda and installation DVD as hdb. Use -boot d to boot from DVD. Don't forget about USB keyboard support!
5) Install the same way, you would install x86 distributive. I used graphic installer. Have you ever installed any OS? I don't think, you'd have some problems.
6) When installer complains, that it can't find installation media - use "specify it manually" option and use /dev/vdb (if DVD is hdb)
7) When installer asks you to use network repository - agree to do it. This way you will avoid future problems with repositories and won't need to add them manually.
Complete installation
9) After reboot you'll notice, that EFI shell refuses to find installation automatically. May be it can be solved some way, but I don't know how. I guess, EFI storage just isn't emulated properly. I don't remember exact names of menu items. Pick 3rd one. Something like "Boot Maintenance Manager" and specify path of one of efi files manually. "/EFI/debian/grubsomething.efi" for example.
10) Boot to Debian. Start Synaptic and go to repositories config. Disable Debian DVD to avoid errors.
11) Just install Lazarus.
12) Lazarus will complain about source version mismatch. Not sure, if it's good way to solve this problem or it can cause some future problems, but I simply changed Lazarus version in file "version.ini" - added "+b2" at it's end.
P.S. I think I know how to solve #9 problem. Will test it tomorrow. First of all -pflash should be used instead of -bios. This will make UEFI area writable. But second pflash image is needed for EFI variables.