mhm?
1 px = 1 pixel
the display resolution of the n900 is 800 * 480 px.
so 64 * 64 px isn't just a dot on the screen.


the first option is to set up a ssh server on your n900 and ssh in from your pc to edit the files on your pc.
just search for "ssh windows" or something - there is even a wiki-thread about this topic.
(best solution for editing files because you can do it via your pc and if something messes up your system you maybe haven't to reflash your device as you can ssh into it and repair what's wrong ^^)

the second option is that you copy the files to a folder which is shown when your n900 is in mass storage mode.
therefore you have to install "rootsh" (for gaining root access to the folders).
if you want to copy the files in a graphical way then you should install "mc" (aka midnight commander).
after that open x-term and type:
1. sudo gainroot
2. mkdir MyDocs/rtcom
then you have the choice:
3. mc
(then you can copy the files from html to rtcom in a graphical way)
or
3. cp /usr/share/rtcom-messaging-ui/html/* MyDocs/rtcom/
4. connect your n900 via usb and check out the rtcom-folder
5. make a backup of these files on your pc
6. edit the files you want to and move them back into the rtcom-folder
(7. if you closed x-term or mc then open it again with sudo gainroot as first command)
8. in mc copy the files back from rtcom to html
or
8. cp MyDocs/rtcom/* /usr/share/rtcom-messaging-ui/html/
9. open any of your conversations, close it and open it again to see what you have done to the file
(10. you can play around with these files or just copy the backup files for returning to default view)

the third option is to edit the files on your n900.
to do that i would recommend you installing "leafpad" (GUI) or "vim" (CLI).
in x-term:
1. sudo gainroot
2. mkdir MyDocs/rtcom_backup
3. cp /usr/share/rtcom-messaging-ui/html/* MyDocs/rtcom_backup
4. vim /usr/share/rtcom-messaging-ui/html/file-to-be-opened.extension
or
4. leafpad /usr/share/rtcom-messaging-ui/html/whatever-you-want-to-edit.extension
5. edit the file and save the changes
6. open any of your conversations, close it and open it again to see what you have done to the file
(7. you can play around with these files or just copy the backup files for returning to default view)