SQL SP to Update 2 records using a value found in a completly seperate table

[ozinm]

OK this may be a bit of a weird one.

Here are my tables:

Table: Relationship
PK: RelationshipID int (Indexed No Dup)
FK: ContactID int (Indexed No Dup)

Table: Contact
PK: ContactID int (Indexed No Dup)
FK: RelationshipID int (Indexed Dup Allowed)

I also have following Local vars:
@Contact1 int
@Contact2 int

How do I create an UPDATE statement that will read RelationshipID in Relationship where Relationship.ContactID=@Contact1 and use it as the value to update the Contact.RelationshipID for all records in Contact where Contact.ContactID = @Contact1 or @Contact2

Hope this makes sense?

Also please let me know if I should post this in the SQL area instead.