I am on fedora core 5
Whenever i try to open a document that i have recieved through e-mail.

An Open dialog box is shown.

It has 3 options:
1.Open it with default application (KWord)
2. Open With..
3. SaveAs

If i select the first option, KWork crashes on opening the document.

Here is the core dump that the application produces.

I want to know why does it crashes??

(no debugging symbols found)
Using host libthread_db library "/lib/libthread_db.so.1".
(no debugging symbols found)
`shared object read from target memory' has disappeared; keeping its symbols.
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[Thread debugging using libthread_db enabled]
[New Thread 1951408 (LWP 2349)]
(no debugging symbols found)
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[KCrash handler]
#6 0x00923848 in Document::Attributes::setRuns ()
from /usr/lib/kde3/libolefilter.so
#7 0x00921f87 in Document::gotParagraph () from /usr/lib/kde3/libolefilter.so
#8 0x00912926 in MsWord::decodeParagraph ()
from /usr/lib/kde3/libolefilter.so
#9 0x009137f7 in MsWord::getParagraphsFromPapxs ()
from /usr/lib/kde3/libolefilter.so
#10 0x009132de in MsWord::getParagraphsFromBtes ()
from /usr/lib/kde3/libolefilter.so
#11 0x00914b4d in MsWord:arse () from /usr/lib/kde3/libolefilter.so
#12 0x00922517 in Document:arse () from /usr/lib/kde3/libolefilter.so
#13 0x0090aa6f in WinWordDoc::convert () from /usr/lib/kde3/libolefilter.so
#14 0x009096d5 in WordFilter::filter () from /usr/lib/kde3/libolefilter.so
#15 0x00900b9c in OLEFilter::convert () from /usr/lib/kde3/libolefilter.so
#16 0x008ff9cd in OLEFilter::convert () from /usr/lib/kde3/libolefilter.so
#17 0x0028d6d7 in KoFilterChain::ChainLink::invokeFilter ()
from /usr/lib/libkofficecore.so.2
#18 0x0028e0ad in KoFilterChain::invokeChain ()
from /usr/lib/libkofficecore.so.2
#19 0x0027a2bd in KoFilterManager::import () from /usr/lib/libkofficecore.so.2
#20 0x0027250d in KoDocument:penFile () from /usr/lib/libkofficecore.so.2
#21 0x0012f82e in KParts::ReadOnlyPart:penURL ()
from /usr/lib/libkparts.so.2
#22 0x00271c01 in KoDocument:penURL () from /usr/lib/libkofficecore.so.2
#23 0x00282532 in KoMainWindow:penDocumentInternal ()
from /usr/lib/libkofficecore.so.2
#24 0x00282482 in KoMainWindow:penDocument ()
from /usr/lib/libkofficecore.so.2
#25 0x002887c1 in KoApplication::start () from /usr/lib/libkofficecore.so.2
#26 0x009e81a0 in main () from /usr/lib/kword.so
#27 0x00dd67e4 in __libc_start_main () from /lib/libc.so.6
#28 0x08048549 in ?? ()

I've seen this many times when trying to open large M$ Word documents with KWord.

You have several options. First you could try updating your kword and hope the latest version has better support for doc format. Alternatively you could open the document with OpenOffice which has great doc support though is really bulky and slow. Lastly, you could try abiword.