This is kind of a general question, but I haven't found an answer yet:

I'going to move my WP blog and ZP installation to a new domain, and I'm at the point of adding a 301 redirect on my old domain.

I found this:

Options +FollowSymLinks RewriteEngine on RewriteRule (.*) http://www.new-domain.com/$1 [R=301,L]
which seems fine for an entire 'copy' of the old site. But I made some modifications:

/folderA/ becomes /folderB/ (the zenphoto installation)
/archives/ becomes /wp-content/uploads/ (all the links within wp-posts to images etc.)

and all the rest stays the same.

So I need three redirections, but I don't know how and in what order.

You need to add those afterward that. It is not exactly a redirection technically, its rewriting the url. It's the same server still, isn't it?

For SEO reasons you should also take care of with and without www ("Duplicate content").

RewriteCond %{HTTP_HOST} ^domain\.com$ [NC] RewriteRule ^(.*)$ http://www.domain.com/$1 [L,R=301]
This redirects calls to domain.com to www.domain.com so it is clear both have the same content.

Yes, the site will remain on the same server.

So would this be ok?

`Options +FollowSymLinks

RewriteEngine on

RewriteCond %{HTTP_HOST} ^spoenk.nl$ [NC]

RewriteRule ^(.*)$ http://www.jacktummers.nl/$1 [L,R=301]

RewriteRule ^archives/(.*) http://www.jacktummers.nl/wp-content/uploads/$1 [R=301,L]

RewriteRule ^beeldend/(.*) http://www.jacktummers.nl/collectie/$1 [R=301,L]`

where
www.spoenk.nl is the old domain, www.jacktummers.nl the new one.
archives/ will be wp-content/uploads/
beeldend/ will be collectie/ (this is the ZP installation)

Since you already rewrite the domain I think you don't need the full domain again.
Actually just this is needed for the url change:
RewriteRule ^category/(.*)?/$ news/category/$1 [L,R=301]
That's an example from our own htaccess file to redirect the outdated Wordpress links.
I am not an real htaccess expert though but that works for us.

Ok, just one more sample then, because it's so important. My old domain existed for ten years , so I don't want to loose any links.

`Options +FollowSymLinks

RewriteEngine on

RewriteCond %{HTTP_HOST} ^spoenk.nl$ [NC]

RewriteRule ^(.*)$ http://www.jacktummers.nl/$1 [L,R=301]

RewriteRule ^archives/(.*) wp-content/uploads/$1 [R=301,L]

RewriteRule ^beeldend/(.*) collectie/$1 [R=301,L]`

Different than the (.*)?/$we use at the end of the first url but best you try it anyway with all sorts of combinations before launching.

One more thing...
If I would also want to add a redirect to a 404 page for visitors, would that line of code have to be BEFORE or AFTER these rewrite rules. And do I have to add RewriteEngine off somewhere?

I don't know right now but I guess that does not matter. Zenphoto uses its own 404 page.
No, RewriteEngine OFF is not need as you want to keep it on, don't you?

Yeah, that makes sense I just thought that placing the errordocument before the rewrite code would make Google skip everything after that (the rewrite rules), thus not using those rewrites.

`ErrorDocument 404 /404.html

Options +FollowSymLinks

RewriteEngine on

RewriteCond %{HTTP_HOST} ^spoenk.nl$ [NC]

RewriteRule ^(.*)$ http://www.jacktummers.nl/$1 [L,R=301]

RewriteRule ^archives/(.*)?/$ wp-content/uploads/$1 [R=301,L]

RewriteRule ^beeldend/(.*)?/$ collectie/$1 [R=301,L]`

how can i redirect my website url to another

This is really not the right forum for your question as is is basic WEB stuff. Please see http://en.wikipedia.org/wiki/URL_redirection