Regular Expression and BETWEEN in same query

Hello,
Could anyone please tell me if there is a way to write RegularExpressions and Between in the same query?
I have a table with a column orderNumber.
The orderNumber has preceeding 0's and .'s something like
"00000034500.1.2.1.1".
There are two input textboxes according to whose values search queries should be fired.
What I would like to do is:
Lets say there are 3 orders with orderNumber "00000034500" ,"00000034600" and "00000034700".
1) If 1 textbox is entered with value "345" and the other is blank I would like to search for the order "00000034500.1.2.1.1"
I am pretty new to DB's, but I suppose I can use a regular expression (REGEX_LIKE) to search this order number(Please correct me if I am wrong).

2) If both textboxes are entered with values "345" and "347"
I would like it to search for all 3 orders.
Is it possible to do this?
Thanks in advance,
Cheers

Also, the length of the orderNumber is not fixed