EDIT:

Ok, I took another swing at it now that I think I have more of an idea of what you're looking for. It isn't perfect, as you can't select specific existing values, but you CAN select a field and enter as many values as you want into the query. Here's the code:

import arcpy
from arcpy.analysis import *

#Define input/output
input = arcpy.GetParameterAsText(0)
fieldName = arcpy.GetParameterAsText(1)
values = arcpy.GetParameterAsText(2)
output = arcpy.GetParameterAsText(3)

#Build the where clause
queryJoin = "' OR " + fieldName + " = '"
whereClause = fieldName + " = '" + queryJoin.join(values) + "'"

Select(input, output, whereClause)

When you set up your parameters, make sure that the field parameter is 'obtained from' "input". Also make sure you select "yes" for multi value for the values parameter.

This will give you something very similar to the example you linked to. I'm sure the query building could be done a better way but my brain is fried. Let me know if this is more along the lines of what you were looking for.

The following arcpy-based script which uses select layer by attributes is a good starting point. I retrofitted the script to work as a script tool in ArcGIS. You can easily substitute polygon FCs for point FCs in the Select Layers section to tailor the script to your specific needs.

# Import system modules
import arcpy
from arcpy import env

# Set the workspace
env.workspace = arcpy.GetParameterAsText(0)
Dir = env.workspace

# Local variables
input = arcpy.GetParameterAsText(1)
polygon = arcpy.GetParameterAsText(2)
expression = arcpy.GetParameterAsText(3)
name = arcpy.GetParameterAsText(4)

# Make a layer from the input feature class
arcpy.MakeFeatureLayer_management(input, "lyr") 

# Select all points or polygons which overlap the polygon/s of interest
arcpy.SelectLayerByLocation_management("lyr", "intersect", polygon, 0, "new_selection")

# Within selected features, further select based on a SQL query within the script tool    
arcpy.SelectLayerByAttribute_management("lyr", "SUBSET_SELECTION", expression)

# Write the selected features to a new featureclass
arcpy.CopyFeatures_management("lyr", Dir + "\\" + str(name))

Using the following parameters:

In this test example,the output includes only the points 1) within the polygons and 2) with "OBJECTID" > 50.

OK - so this is what I've come up with so far. It kind of works. Its going through the whole process but only giving me back the first county that I list as an argument. For example, when I type in county names in the arguments dialogue box I've tried typing it "ASHE";"AVERY" as well as "ASHE" "AVERY" and the script only takes in ASHE. I'm assuming this might be a syntax issue? Here is my current code:

 def whereClause(table, field, values):
    """Takes a semicolon-delimited list of values and constructs a SQL WHERE
    clause to select those values within a given field and table."""


# Add field delimiters
fieldDelimited = arcpy.AddFieldDelimiters(arcpy.Describe(table).path, field)

# Split multivalue at semicolons and strip quotes
valueList = [value[1:-1]
             if (value.startswith("'") and value.endswith("'"))
             else value for value in values.split(';')]

# Determine field type
fieldType = arcpy.ListFields(table, field)[0].type

# Add single-quotes for string field values
if str(fieldType) == 'String':
    valueList = ["'%s'" % value for value in valueList]

# Format WHERE clause in the form of an IN statement
whereClause = "%s IN(%s)" % (fieldDelimited, ', '.join(valueList))a
return whereClause


def outName(input,post="Out",fileExtension="shp"):
    """Returns output name."""
    outName=os.path.basename(input).split(".")[0]+post+"."+fileExtension
    return outName 

Select County(s)

InputFC = "C:/Project/ToolData/CountyBoundary.shp" 
Field = "CO_NAME"
Counties = arcpy.GetParameterAsText(0) #user selects counties from choice list
SQL=whereClause(InputFC,Field,Counties)
OutputFC=outName(InputFC,"_Select")
arcpy.Select_analysis(InputFC,OutputFC,SQL)
count=int(arcpy.GetCount_management(OutputFC).getOutput(0))

print OutputFC, " was created, and contains the following", count,"counties:"

sc = arcpy.SearchCursor(OutputFC)

for line in sc:
    print line.CO_NAME