You should be able to create an export file which includes entry tags and entry basenames for subsequent import into a Movable Type 4 installation by creating a new index template in the Movable Type 3 installation, then copying the following code and pasting it into the new index template:
CODE
<MTEntries lastn="999999">
AUTHOR: <$MTEntryAuthor strip_linefeeds="1"$>
TITLE: <$MTEntryTitle strip_linefeeds="1"$>
BASENAME: <$MTEntryBasename$>
STATUS: <$MTEntryStatus strip_linefeeds="1"$>
ALLOW COMMENTS: <$MTEntryFlag flag="allow_comments"$>
CONVERT BREAKS: <$MTEntryFlag flag="convert_breaks"$>
ALLOW PINGS: <$MTEntryFlag flag="allow_pings"$><MTIfNonEmpty tag="MTEntryCategory">
PRIMARY CATEGORY: <$MTEntryCategory$></MTIfNonEmpty><MTEntryCategories>
CATEGORY: <$MTCategoryLabel$></MTEntryCategories>
DATE: <$MTEntryDate format="%m/%d/%Y %I:%M:%S %p"$><MTEntryIfTagged>
TAGS: <MTEntryTags glue=","><$MTTagName quote="1"$></MTEntryTags></MTEntryIfTagged>
-----
BODY:
<$MTEntryBody convert_breaks="0"$>
-----
EXTENDED BODY:
<$MTEntryMore convert_breaks="0"$>
-----
EXCERPT:
<$MTEntryExcerpt no_generate="1" convert_breaks="0"$>
-----
KEYWORDS:
<$MTEntryKeywords$>
-----
<MTComments>
COMMENT:
AUTHOR: <$MTCommentAuthor strip_linefeeds="1"$>
EMAIL: <$MTCommentEmail strip_linefeeds="1"$>
IP: <$MTCommentIP strip_linefeeds="1"$>
URL: <$MTCommentURL strip_linefeeds="1"$>
DATE: <$MTCommentDate format="%m/%d/%Y %I:%M:%S %p"$>
<$MTCommentBody convert_breaks="0"$>
-----
</MTComments>
<MTPings>
PING:
TITLE: <$MTPingTitle strip_linefeeds="1"$>
URL: <$MTPingURL strip_linefeeds="1"$>
IP: <$MTPingIP strip_linefeeds="1"$>
BLOG NAME: <$MTPingBlogName strip_linefeeds="1"$>
DATE: <$MTPingDate format="%m/%d/%Y %I:%M:%S %p"$>
<$MTPingExcerpt$>
-----
</MTPings>
--------
</MTEntries>
When this index template is rebuilt, it should generate an export file containing entry tags as well as entry basenames, which Movable Type 4's Import feature does recognize but Movable Type 3.35 does not. However, private entry tags (entry tags beginning with "@") will not be included in the export file due to a limitation in the Movable Type 3.35 code. Also, only entries with a status of Published will be exported - entries with a status of Unpublished or Scheduled would not be included in the custom export file.