Lightbox in greypop-- can't find instructions that are rudimentary enough for me.

I've gathered that I need to redirect image paths to get lighbox to work in the greypop theme, but I can't find instructions that I understand. Do I access the info from my ftp program? Once there, what exactly must I do? I read somewhere that light box won't work if the image isn't at least 600 px. Is that true? Does that refer to total pixels, or the size of one side?

Also, I'm wondering if there's a place I can type in a title for the header (as appears in the demo) or do I need to modify the header image myself?

Sorry if these have been answered before, but I've spent lots of time sifting through all this info, and haven't found what I was looking for. Thanks for the help!

Gallery version = 2.2.2 core 1.2.0.4
PHP version = 5.2.5 cgi-fcgi
Webserver = Apache/2.2.6 (Unix) mod_ssl/2.2.6 OpenSSL/0.9.8g DAV/2 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635
Database = mysqlt 5.0.45-community-log, lock.system=flock
Toolkits = ArchiveUpload, Dcraw, Exif, Getid3, LinkItemToolkit, Thumbnail, Gd, ImageMagick, NetPBM
Acceleration = none, none
Operating system = Linux host168.hostmonster.com 2.6.22-9_1.BHsmp #1 SMP Sun Feb 10 15:57:22 MST 2008 x86_64
Default theme = greypop
gettext = enabled
Locale = en_US
Browser = Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8.1.12) Gecko/20080201 Firefox/2.0.0.12
Rows in GalleryAccessMap table = 22
Rows in GalleryAccessSubscriberMap table = 11
Rows in GalleryUser table = 2
Rows in GalleryItem table = 9
Rows in GalleryAlbumItem table = 3
Rows in GalleryCacheMap table = 0