Yes, this is possible but it is confusing to set up especially of you have not set up a many to many relationship before. i just did one myself a week ago and it worked fine. You may want to contact me off line for assistance if we can't communicate well enough here.
You will need to set up one additional table called Artist Gallery Connections.,
I imagine that you have multiple choice field indicating whether the Account is an Artist or a Gallery.
Make a Relationship where 1 Account has many Artist Gallery Connections. Rename the field from [Related Account] to be called [Related Gallery]. Lookup the field for Account name and rename it to be called [Gallery Name]. Check the field properties for the field [Related Gallery] and ensure that the Proxy field is set to Gallery Name.
On the form for the field [Related Gallery] there will be a drop down field to choose an Account. Make a report filtered for just galleries as a drop down list. Edit the form properties ot use that report so that when you select an "Account" you will only be offered a list of Galleries.
Now ....repeat for Artists ...
Make a Relationship where 1 Account has many Artist Gallery Connections. Rename the field from [Related Account] to be called [Related Artist]. Lookup the field for Account name and rename it to be called [Artist Name]. Check the field properties for the field [Related Artist] and ensure that the Proxy field is set to Artist Name.
On the form for the field [Related Gallery] there will be a drop down field to choose an Account. Make a report filtered for just Artists as a drop down list. Edit the form properties ot use that report so that when you select an "Account" you will only be offered a list of Artists.
