Can a transaction safely guarantee this?

[Matt Houser]

I have two tables:

Groups:
GroupId: int (auto increment)
GroupName: varchar
IsDeleted: bit

Items:
ItemId: int (auto increment)
ItemName: varchar
GroupId: FK into Groups table
IsDeleted: bit

For record keeping, I do not want to actually delete Groups and Items, so instead, I have an IsDeleted flag for each.

My business logic says that all non-deleted items must reference to a non-deleted group. If a group is deleted, then all referring items must be deleted at the same time.

Can a transaction guarantee me that someone won't be creating a new item and assigning it to a group at the same time that I am deleting a group?

If in my "insert" transaction, I do a select on the group id to verify that IsDeleted = 0, will the transaction protect the record from update by the "delete" transaction?

Thanks,
...Matt