Changing cell color with either conditional formatting or macro

Excel 2003 or 2007, 3 preferred.
I have a column 'E' that contains either 2 or 4 digit text codes (MR, SP, BA SC, EU WO, etc), up to 50 unique codes. I need to highlight cells based on specific content (MR, EU WO, RG, etc., but not HM, HM CG, WO, etc.). Color of cell is not important, just not white. This is for quick visual identification so that I can perform other actions on that information while leaving the 'white' cells alone.
In 2003, using Conditional Formatting, I have had success with the following formula:
Cond. 1 = Formula is
=NOT(ISERR(SEARCH("MR",E1)))
Choose cell color RED
Problem arises because you are limited to 3 conditions in 2003. Question then is:
Can you modify the formula to search for more than 1 unique code at a time?
I have tried =NOT(ISERR(SEARCH("MR","RG",E1))) with no luck. Is my syntax wrong? Like the comma between the search items "MR" and "RG". What should it be? Or am I barking up the wrong tree? As may be potentially obvious, I know just enough to hurt myself with a spreadsheet... I use this on a daily basis and would really like to figure something out. My poor little mouse is tired out! This spreadsheet changes on a daily basis (daily order from 1 customer) and can contain upwards of 150 rows. The row info referenced by column 'E' needs to be separated for invoicing purposes, as well as order entry. Thanks, in advance, for any help someone may be able to offer.

Edit: So, OK. In 2007, it is possible to create a macro that starts 'X' number of conditional formatting instances that take care of what I need. I was hoping that something more elegant might be available. Also, something that would work in 2003.

Edit (2): In 2003, Conditional Format does not seem to allow me to run more than the 3 applications allowed. If, for instance, you make condition 1 through 3, then start a new instance of CF (like you would record a macro to manage multiple sorts) whatever changes you make to Condition 1 removes the formatting from the cell originally referenced in Cond. 1 and applies it to what could be considered Cond. '4'. Hopefully, I have not muddied the waters and someone is willing to shine a light my way. Thanks again!