T-SQL (SS2K8) :: How To Ignore Between Operator End Value If It Is 0 In Where Clause

create table deltavalues (planid varchar(10), baseval float, highval float)

Insert into deltavalues values ('1002', 2000,5000)
Insert into deltavalues values ('1003', 1000,0)
Insert into deltavalues values ('1004', 500,0)
Insert into deltavalues values ('1005', 1000,2000)

--I have below query , basically getting emnployee table balance between deltavalues table baseval column and highval column

select * from employee e join deltavalues d on e.planid = d.planid
where e.balance between d.baseval and d.highval

but here what i am requesting you is how can i change the highvalue to not include if it is 0

for example above example plan 1003, 1004 has highbal as 0 so i want to write a query to get employee data between 1000 and anyvalue (> 1000 - no limit)

same way for 1004 between 500 and no end values (infinity)